Tanjiro stared at Tamayo-san's neutral face as her words sank in.

"The more you use that power, the more you will revert to being a demon."

His breath caught in his throat and he looked down at his hand again. It still looked human… but for how long? Really, he should have expected something like this. But it still… hurt. He'd enjoyed being human again. He liked being able to eat rice and seaweed and fruit. He loved that he could walk under the sunlight without repercussions. Not having Muzan looking over his shoulder every single second? Fabulous!

But it seemed now that this reprieve wouldn't last. Really, he should have known.

He'd come to Tamayo-san knowing that something was off. He'd helped her with her work on analyzing his blood in both his human and demonic state. It hadn't been easy, but he'd managed to get himself to transform to give samples by thinking about the fight with Enmu and trying to imagine himself back on the boat. Slipping into that state like he had worried him, not because he couldn't control it (he hadn't had an issue with that, even if it had almost felt hazy, he'd still been fully cognizant of his actions) but because he was worried that Muzan would gain a connection to him again, despite him not seeming to be subject to the curse.

He'd brought the worry up to Tamayo-san and they'd tested it carefully. It turned out that he could still say Muzan's full name when transformed (if one could really call it a transformation), but the longer he remained in his demonic state, the more the feeling he shouldn't continue grew, eventually reaching a point where he simply didn't dare. Once he dropped out of the state again, the feeling had vanished.

No one had any illusions as to what that meant.

He couldn't let Muzan get any memories of his previous lives. That was what had led to his most recent loop… He couldn't handle another one like that. People called him 'resilient' when he continued to care about the beings who had hurt him and his family so badly, but everyone had their breaking point. He knew what his would be; Muzan somehow finding his family and forcing him into servitude again. The very idea almost sent him into what Tamayo-san called a 'panic attack'. They were aptly named. It was a sort of quiet panic instead of Zenitsu's loud shrieks or Inosuke's angry screams – the kind that built in his chest and stopped him from being able to breathe or care or think.

That state of mind, more than anything else, scared him, to be honest. Demon or not, he wasn't sure he could control himself with that kind of panic eating at him.

Tamayo-san had told him that if he happened to have such a panic attack during a fight, that he needed to slow down and count his breathing. He told her he shouldn't have a problem with that because if he was in a fight, he'd certainly be using total concentration breathing. He tried to do so constantly anyway. So she told him that feeling someone else breathe slowly can help as well and that he needed to concentrate on what he could sense in the moment. The one time he'd had to use the information, she'd walked him through it, talking about what he could feel and taste and see and smell. It had helped. A lot.

Fortunately, he didn't need to use it now, but it was a near thing. Taking a deep breath and then returning to the total concentration breathing, he looked up at Tamayo-san.

"I thought you said the blood you took when I was human looked perfectly normal," he tried not to sound accusing, but he needed to understand.

Yushiro looked about ready to tackle him for simply asking the question (although if he did so at this point, he'd be reminded why that wasn't a good idea via unconsciousness – Tanjiro was very much not in the mood right now).

Tamayo-san sighed, then nodded, interrupting whatever Yushiro had been about to say (thankfully). "It does, for the most part. However, after some studying, I did find some demonic cells."

Tanjiro blinked, mind barely processing that.

"How?" he finally asked. From studying with her in previous loops, he knew that Demons had blood similar to a human's, but their cells were fundamentally different. Muzan's cells acted very much like a virus, invading the cells of the human and changing them. It was how the cells changed that tended to give demons their blood arts, and Muzan's cells interacted differently with each host. Tamayo-san had always commented (rather grudgingly) that it was an interesting, if horrible, process to observe. However, a balance between the human and demon cells had to remain as the demon cells couldn't seem to function on their own. At least, not initially. Eventually, once they, too, adapted to their host, they could act as cells the body needed, regenerating quickly and efficiently, thus halting aging and encouraging regrowth. That initial struggle for balance was why some humans couldn't handle Muzan injecting his blood or injecting too much blood into them. It was also why demons woke up so hungry. The demonic cells wanted more human cells to devour and invade.

Demonic cells existing next to human cells without one attacking the other shouldn't be possible.

When Tamayo-san remained silent, seemingly lost in her own thoughts for a moment, Tanjiro pressed.

"How can I have demon cells inside of me that aren't attacking the rest of me? Isn't that what demon cells do? And how can I have demon cells inside of me at all?! I haven't even come in contact with Muzan or any of his Waxing Moons!"

Tamayo-san just shook her head, having come out of her thoughts at his question. "I don't know, Tanjiro-san," she said quietly. "In all my years, I have never seen anything like this before. The demonic cells in your blood as a human seem to have already mutated to fit your body, however, they aren't attacking any of your normal cells when you are human. It took me a while to find them at all, but once I knew what to look for, I did indeed find them in small amounts. They seem stagnant – dormant even – and in such a state would have little to no effect on your body."

She paused for a moment, taking a sip of her tea. Tanjiro just continued to wait, hands in fists as he tried not to worry.

"That was what I learned from your first human sample," she finally continued, expression still neutral. "However, in your demonic state, the cells multiplied ten-fold at least. At that point, they did attack some of your human cells, although not at the rate I would have expected. The sample taken after you reverted back to your normal human state looked much like the first sample. I don't know where the extra demon cells vanished to. I don't know if they merged or simply disappeared altogether… however, while it wasn't an enormous increase, there were more of them from that second human sample.

"The only conclusion I can come to is that the more you use that power, the more you will slowly transform. Eventually it will reach a point where even reverting back to a normal state won't erase enough demonic cells. When they reach a point where they permanently outnumber your human cells, you will have become a demon again.

"As for an explanation… I can theorize you are somehow, subconsciously, tapping into your demon blood art and reaching back through time to your other lives for the extra strength your body feels you need to finish a battle, but it is just a theory."

In Tanjiro's experience, her theories tended to be pretty close to truth. He grit his teeth. "I became complacent," he finally said. "Relying so much on demonic strength that my body doesn't know how to fight without it anymore."

He felt sick and angry. Sick at the fact that he hadn't escaped the curse after all – that Muzan's mark on his soul had somehow continued on through time and brought his cursed cells with it; angry at himself – his subconscious – for allowing it and relying on it to a point where he couldn't even be completely human when he went back in time.

"I still think," Tamayo-san said slowly, drawing him from his spiraling thoughts, "that you will be our best chance at fighting him. And I still think that the information I have gained from your blood can help me develop a cure – or at least a stop-gap measure."

Tanjiro looked up at her, unable to keep the hope he felt at her words from showing on his face.

For the first time since the conversation began, she smiled at him, soft and small. "I don't know how long it will take, but I will most definitely work on it as often as I can."

"Be grateful Tamayo-sama is using her precious time for you!" Yushiro said, apparently unable to keep his frustration back anymore.

Tanjiro realized she may have a more difficult time developing a cure simply because his circumstances were so unusual, and once again he felt immensely grateful he'd met her in his first life.

"H-hai!" he said, hoping that she understood how grateful he was. Just in case she didn't, he bowed his head deeply. "Thank you for your help, Tamayo-san! I cannot express the depth of my gratitude!"

Yushiro snorted lightly, seemingly appeased and Tanjiro looked up warily. He'd returned to kneeling calmly, tea in hand. Tamayo-san looked fondly annoyed at him, and Tanjiro found himself grinning a little. Their relationship rarely changed and it was a constant he could definitely appreciate.

"In any case," she said, turning back to her guest. Tanjiro sat up straight, listening intently, "I must reiterate this, Tanjiro-san: You need to realize that you can only use that power in the most dire of circumstances. The more demon cells in your body, the more demon-like tendencies you'll have, even as a human. If you use that form too often, you will risk falling to Muzan again."

He didn't really need that reiterated, but she wasn't wrong.

He nodded firmly at her. "Hai, Tamayo-san. I'll remember that!" Of course, unless he came across one of the Waxing Moons or a particularly large group of demons, he doubted he'd have to resort to that.

She sent another smile at him and Tanjiro ignored the jealous glare Yushiro sent him.

"In any case, since you do have demonic cells in you, I'd recommend you take the rest of the time you have here to sleep. Your demonic cells have already adapted to your body, but with some of the side effects we've witnessed, they may need time to change as they have in the past reiterations you've spoken of."

Tanjiro blinked. He hadn't thought of that. Well… he did have an undisclosed amount of time off from his demon slayer duties… how much time could he spend here? Would it help at all?

"Although, I do have one more request of you…" Tamayo-san ventured carefully.

Tanjiro blinked, then looked up and thought back over their conversation. Than he smiled at her.

"You want me to gather blood from the Twelve Kizuki to help you with your research because they have the most amount of Muzan's blood."

"How dare you presume to know Tamayo-sama's mind?!" Yushiro shouted.

Tanjiro ignored him, grinning at his hostess instead. She blinked, then smiled again. "Exactly."

Yushiro's head whipped around, looking betrayed.

The time-traveler put a hand up to the back of his head, rubbing it thoughtfully. "I don't know how long I can stay, but let me write to Ubuyashiki-sama and tell him about some of the Waning Moons I know about. He can set up a time for multiple demon slayers to strike. I'll rest here until I have to leave for that… if that is alright with you, of course."

The green-haired boy had opened his mouth to say something, but closed it with an angry snap when Tanjiro bowed to Tamayo-san again.

"That seems more than acceptable in trade for the information you have brought to me," she said softly. "Did you bring your kasugai crow with you?"

Tanjiro nodded. "I did. I just need some paper, a brush and an ink stone to write to Ubuyashiki-sama. If we go now, we may be able to get to some of them before Muzan kills them all off."

"Of course," Tamayo-san said with a nod of her head. "Yushiro," she turned to the boy by her side, "please go and get some writing supplies."

He glared once more at Tanjiro before turning to Tamayo-san, practically sparkling. "Hai, Tamayo-sama!"

Tamayo-san didn't sigh, but that fondly exasperated expression had returned.

Tanjiro just grinned.

An hour later, he walked outside of Tamayo-san's house and whistled. Immediately, his crow (different than the one he remembered from his first life – quieter, for which he was grateful) came to him and he handed the letter to him.

"When you bring a reply, come back here and just head straight over the fence," he instructed, pointing to the supposedly unbroken fence behind him. "You'll find a large building on the other side with some demons inside. They won't hurt you. I give you my word.

"I've updated Ubuyashiki-sama on several things, so it is extremely important that he gets this as soon as possible. Understand?"

"Caw, yes!" the crow said.

Tanjiro smiled. "Great! I'll await your return. Fly safely."

"Caw!" he said and rose into the air. Tanjiro watched him go before he returned inside where Tamayo-san had asked Yushiro to prepare some food for their guest. He thanked the boy and choked the over-cooked rice and fish down without complaint. (It was, after all, better than other things he remembered eating.)

Yushiro just sort of sulked at him, watching while Tanjiro cleaned his dishes and then asked Yushiro to inform Tamayo-san he would be retiring for an unknown amount of time. He hadn't tried to sleep longer than one night this time and while part of him hoped he could, part of him hoped it would all prove to be unnecessary. Still, better safe than sorry.

Once in his room, he went through his nightly routine, wrote a letter to Nezuko and his family that he would ask his crow to take once he returned, before laying down on the futon and eventually drifting off.

xXx

Tanjiro woke four days later.

That both worried and relieved him.

Worried him because it was necessary, relieved him because it meant his body still could change if he ended up becoming a demon again.

He'd still prefer that that didn't happen… but he'd long ago decided that if that was what he had to do to keep his family safe, then he would. He also didn't feel any different and didn't know what to make of that. Usually he could feel something had changed when he woke up, but it had only been four days.

And was he hungry… he hadn't eaten at all in that time…

Yushiro had woken him by rudely shaking him (Tanjiro still thanked him) and thrust a letter from Ubuyashiki-sama at him.

"Your crow wouldn't stop making noise! Tell it to be somewhat respectful next time!"

Tanjiro just grinned. He'd admitted that there would be a next time. "Hai!" he replied.

Yushiro just scowled and stomped out of the room, leaving Tanjiro to open his letter. First, it thanked him for his information and then let him know that he had put together a group of demon slayers to send against Mt. Natagumo. Then it asked him to go along, of course, to meet a Pillar and a demon slayer ranked kinoe (who happened to be on the verge of becoming a Hashira) at the end of the week. They would be leading the contingents of demon slayers against Rui's nest of Tsuchigumo. It would take him about that long to make it to the rendezvous point if he didn't want to rush, which meant he'd have to leave as soon as possible.

Also, apparently for defeating Waning One, he'd been promoted to Kinoe as well. Huh. He didn't even remember what rank he'd reached his first life as it hadn't really mattered. He'd just tried to be as strong as he could, and that was that. Still, he appreciated the appointment and thanked Ubuyashiki-sama in his confirmation letter before sending that and his letters to his family with his kasugai crow.

Tanjiro smiled as he set off that morning, bidding Tamayo-san and Yushiro farewell. Tamayo-san wished him well. Yushiro told him good riddance but he'd better come back alive for Tamayo-san's research – and to watch out for their cat.

Tanjiro smiled, knowing that was the boy's way of wishing him well too. It was nice to know that human or demon, he could count on these two as allies. It was a good feeling.

He stopped on the way out of town at a restaurant and ate far more than he normally would have, but figured that four days of sleeping for a human – even if he did have demon cells inside of him – was pushing it.

He also picked up some rice balls for the road. Not a half-hour on his way, his stomach growled and he picked out a rice ball to snack on. By the time noon rolled around, he'd eaten all of them already.

"Huh, I sure have eaten a lot today," he said to himself. "I wonder why I'm so… hungry."

The more demon cells in your body, the more demon-like tendencies you'll have, even as a human.

He stopped on the road, hand on his growling stomach. For several seconds he just stood there, but eventually he shook his head. "No. It's just because I slept too long. That's all."

He'd pick up some extra food when he reached the next town. If he hurried, he could get there in time for a long dinner. He had enough money. He'd just gotten paid. Besides, Kanroji-san ate a lot too, didn't she? And she was fully human, right? He didn't even remember how much he'd eaten at meals the first time, so maybe it was pretty normal for someone learning a breath style. Rengoku-san had eaten a lot of food too. Yeah, that was it.

He took off his conical hat as he pushed on, happy to feel the sun on his head not burning him to death, determined to get to the next town and eat hotpot until he burst.

xXx

"I don't care," Rui said in his monotone voice. "Now get off my mountain."

Silence for just a few seconds and then a cacophony of noise.

"What do you mean, you don't care?"

"You think you can just barge in here—"

"How can you say that?"

"—and just demand—"

"Do you want to die?"

"You immature brat!"

"Don't talk to Rui-sama like that!"

"LEAVE NOW!"

"QUIET!"

Rokuro shouted, having activated his blood art two tails to make sure they understood the threat in his voice. Thankfully, everyone listened to him. Probably a good thing for them, he was running out of patience and he outranked everyone there.

Slowly, he allowed himself to shrink back down and his facial markings to fade back to the normal vein-like pattern that had stuck around since he'd gained his position as Waning Moon Two. He breathed out, his mind coming back to him and he eyed every one of the two dozen or so demons before him, trying not to show his disgust.

This was why demons weren't supposed to form groups. They just didn't work well together… except when they had to, apparently. Or when Lord Muzan required it. And of course that lousy Enmu had gone and gotten himself killed, leaving Rokuro to pick up the pieces. (Not that he was really complaining, but it had been unexpected.)

Still, the expression of fear from most of the demons and wariness from the rest of the Waning Moons made him want to smile. He wasn't used to being in charge of a group, but that didn't mean he couldn't enjoy it instead of being the one on the bottom. He would make sure they would win this battle, even if he had to drag them kicking and screaming to victory.

Rokuro remembered the recent meeting with Lord Muzan, remembered suddenly finding himself in the tunnels underneath the town he preferred to haunt afterwards, hand reaching for his still intact neck as he breathed hard. He remembered realizing that he could have done absolutely nothing if the demon progenitor had decided they were too weak and worthless. He'd only just made it into the Waning Moons and he'd thought it such an accomplishment… but now he realized, as he always had, that it wasn't enough. It would never be enough until he held the top position and no one could hold anything over him ever again.

He hadn't expected to leave that meeting alive. He hadn't been the only one either. In all honesty, Rokuro hadn't been sad to see Enmu go, but instead of promoting them all a number, Lord Muzan had told them that he'd give them one final chance to catch the demon slayer boy with the red eyes and hair. If they succeeded, not only would they live, but he'd also give anyone surviving more of his blood. Then he'd strongly recommended they work together and given them a month to accomplish the task.

Rokuro had known from the get go that it wouldn't be easy to herd the Waning Moons into something remotely cohesive, let alone find the blasted demon slayer to begin with. Their normal methods of finding a place and picking off their meals as they wandered or were lured into traps wouldn't work. They'd had to be active.

So Rokuro had hunted down each and every one of the Waning Moons and they'd been reluctant but desperate enough to join forces and share information.

They'd all started to get antsy when two weeks had gone by without a single lead. But then Mugako, Waning Four, had overheard a conversation between a group of demon slayers leaving her town and managed to pick up on their new assignment – an assault on Mount Natagumo. Apparently, many demon slayers were being called off their current missions for said assault and she'd even managed to get the date.

It would be their last best chance at finding the red-haired boy and a great opportunity to take out a bunch of demon slayers while they were at it. So she'd come to Rokuro, who had picked up a surly Wakuraba and the skittish new Waning Six, Kamanue before heading to Rui's mountain.

And now he wanted them to leave.

What utter ridiculousness.

On one side of the room, Rui and his 'family' stood, looking about ready to attack or run (if they were smart, they'd choose the latter over the former) and on the other side stood the other four Waning Moons.

This… was so not his day. Why didn't people just listen to him?

He took a deep breath and tried to keep calm. "Rui," he said slowly (no one interrupted, so no one died, smart of them), "you realize that several demon slayers and likely even Hashira are coming to your mountain. They will kill you all."

Uneasy shifting from the rest of the Tsuchigumo, but the youngest-looking of them stood his ground utterly calm – almost bored.

"This mountain is mine and my family's. It is ours to protect. We don't want you here."

Behind him, Mugako grit her teeth, and let out a 'tch' sound. He saw Wakuraba roll his eyes out of the corner of his vision and Kamanue shifted uneasily, hands full of paper dolls. He pinched the bridge of his nose, refusing to let this all devolve into a fight.

"You don't understand, Rui," he finally said, tone hard as steel. "We're not asking to stay. We will stay. Period."

That got a reaction out of the boy. He grit his own teeth and stepped forward angrily. "Don't get involved in family matters!"

Rokura laughed aloud at that. Oh, this was almost cute, him thinking he could take Waning Two with his band of misfit spider demons?

"Family. Yeah, sure, whatever, kid," he said, still chuckling. "But I can't say that I care. The only thing I care about is fulfilling Lord Muzan's wishes and not dying – something you don't seem to care about." More shuffling from the spider demons, but he didn't even bother to tense up. If they attacked him, they'd die. End of story.

"I will fulfill the request on my own. With my family," the white-haired kid insisted.

Mugako laughed this time. "Right, because your entire family can potentially stand up to the person who killed Waning Moon One?" She nudged Rokura in the side. He had to remind himself that he really shouldn't kill her too. "He's so funny! I wonder if he does parties."

"Don't talk about Rui-sama like that!" one of the spider demons, a petite woman with an ample chest and long, white hair, stepped forward.

"Mother," Rui said softly, his voice quiet.

The woman eeped and stepped back, looking chastised.

"Che, this is a waste of time," Wakuraba said, rolling his head and popping several joints in his neck. "If the kid wants to die, fine. Let him. We can ambush the slayer corps scum on the way out."

Several people spoke up at that, from both sides, but Rokura thought about the suggestion. It… wasn't a bad idea. Just needed a little tweaking here and there…

Yes… that could work.

"Fine," he finally said loudly over the din. Once again, everyone stopped, leaving the quiet for him to fill. He could definitely get used to that. Maybe Rui had the right of it after all by getting himself a bunch of subordinates (even if he passed them off as his fake family)? Huh. He'd have to think on that.

Later. When he earned more of Lord Muzan's blood.

For now, he had demons to corral.

"You and your demons take this side of the mountain. We won't interfere unless we see the red-haired, red-eyed kid. You act as a distraction for everyone else coming, we'll capture him and take him to Muzan, everyone's involved, everyone gets the reward, everyone's happy. What do you say, brat?" Rokura raised an eyebrow, daring him to refuse. This was him being nice.

Finally, Rui stood straight and nodded. "Acceptable."

Rokura nodded once and turned to walk out. "We'll find a suitable place to watch. Good luck with the corps, brat."

And with that, he led the other Waning Moons (besides Rui, of course) out of the decrepit house. They didn't have a lot of time before sunrise and would have to find a decent place to hole up. He thought he'd spotted some caves a couple of miles north, on the other side of the mountain.

"Huh, didn't expect you to give in like that," Wakaruba said once they'd gotten far enough from house that no one would be listening in.

Rokura snorted. "If you think that was me giving in, then no wonder you haven't beat me."

The Waning Three glared angrily, but before he could say anything, his superior went on.

"The brat wants to face the corps alone? Fine. Betting there will be a Pillar or some of the higher-ranked ones in there. Let his 'family' distract all of them while we keep an eye out for Lord Muzan's prize." He paused. "Remember, he wants the kid alive."

"But why?" Mugako whined.

"You wouldn't want him anyway," Wakaruba said. "He's a demon slayer, so he doesn't work for the government."

Rokura noticed the very quiet Kamanue's expression darken. Right, the brat actually liked the current government. The Waning Two didn't really see a point either way. A human was a human. Admittedly, he himself tended to like going after higher-class people, so he probably couldn't talk. Still, at least he preferred cattle who were well fed, not worked to the bone.

He didn't really know what kind of human Kamanue preferred. Not that he particularly cared.

"I don't mind a demon slayer either," Mugako said back, eyes dreamy. "I'll bet he'll taste so good…"

"No, he won't," Kamanue finally cut in harshly. "Didn't you hear a word Rokura-san and Muzan-sama said?"

She snorted. "Of course I did, Six," she returned disdainfully. "I can control myself. Unlike some people."

He snarled at her. "Like you know anything about me."

She just giggled cruelly. "I've seen you around your preferred age… what is it, 40? 50? Men or Women… you tear them apart."

"Like you're any better, Shogun-supporter!"

"You say that like I support any government," she replied cheekily.

The brat looked ready to attack her at any moment.

"We need to pick up the pace if we want to make it to a cave by sunrise," Rokura cut in, wanting to keep everyone on track. "Besides, who cares how the humans govern themselves as long as we're loyal to Lord Muzan."

"But I do so love a man in uniform," Mugako replied sweetly, licking her lips hungrily.

Kamanue threw several paper dolls at her, but before they could even get half way, Rokura stopped them by cutting them down and halting their momentum.

"That's enough! We are here for one purpose and one purpose only. If you can't even get along now, how do you expect to fight without getting in each other's way? So you. Will. Shut. UP. Before I have to kill one of you to shut you both up. Understand?"

Behind them he could see Wakuraba snickering quietly.

Four and Six eyed each other before Mugako turned away and shrugged. "Fine. Whatever," she said as she walked away

Kamanue just harrumphed and went back to sulking and playing with his dolls, watching the little things flutter around him in an impressive dance.

Honestly, they were worse than children!

This… would be a long few days.

xXx

AN: SO! Yes! Here are my takes on the Lower/Waning Moons. I will admit, there wasn't a lot to go off of, but between Tim, Quathis and I, we were able to come up with something I'm pleased with. I'd be more than happy to post their bios after their next fight. Would anyone be interested in that? Thoughts?

Thank you to Quathis and TimeLordTim! You guys rock!

Discord: discord. gg/EVUrHMd4za (no spaces)