This is inspired by Taisi's one-shot "Okay, Someday." So though some consepts are mine, the whole idea behind it was inspired by Taisi.

Harley could feel her presence as the girl entered the camp, well he heard her dogs barking at least. "Jake, she's home," the boy told him. Jake looked at his youngest half brother, balancing on his crutches. His wavy brown hair fell in his face, trying to figure out who the younger demigod was referring to. Then it hit him. Hades' daughter. His only child born after the pact was broken by Zeus, well, known.
"Harley, keep her occupied, make sure she doesn't find Leo," Jake told the black haired Native American. He nodded, running out of the forage. This was not good. Lucifer couldn't be back, not now that Leo was here.
After Beckendorf died, after the war, she left with three requests for him. "Don't let Luke be looked at as a traitor, he's still my brother, he just made bad choices. Don't let anyone have Beckendorf's bed. And don't give up your counselor position. Promise me that." Jake had been stupid enough to promise her that. He'd kept one of the three, Luke wasn't looked at as a trator, at least people didn't voice it, especially around the Hephaestus cabin, who were told to punch anyone who said anything about Luke they didn't think Luce would take well if she was here.
Jake thought she'd be gone longer though, possibly a couple years, not months. But nope here she was at Camp Half-Blood in January, around four months after she disappeared. Shit was not going to turn out good.

Harley ran as fast as he could, dodging demigods and satyrs on his run to meet Hades' daughter. She was walking towards the camp, a black dog that's back was to her mid-thigh. Lucifer had had that dog, a black Peruvian Inca Orchid/German Sheppard mix named Cerberus (yes, after her father's dog) since her half-brother, Nico, and half-sister, Bianca had come to camp. On Cerberus' back was a little black dog, maybe three months old, with white patches. Next to her foot was a red-brown puppy that barely cleared her mid-calf at the head. The son of Hephaestus pushed himself faster until he had reached her.
"Hey Harley," she said, petting his head when he wrapped his arms around her waist. The brown puppy jumped up on Harley, wanting attention. "Beckendorf, down." The puppy backed down, sitting and looking at her and Harley.
"Come on we need to tell Chiron you're back, plus you need to meet Jason, your cousin," Harley told her.
Lucifer nodded, following the young son of Hephestus to where ever he was leading her.

Leo would have slept peacefully if it wasn't for the sudden sound of a girl screaming. At Jake. "WHAT IN THE NAME OF MY FATHER!" She yelled, jolting Leo out of his much needed sleep. He was always working on the Argo II so he rarely got any sleep, ever.
"Lucifer, calm down, you're going to wake up everyone," Jake whispered in a harsh tone.
The girl, Lucifer, growled, but started to whisper back, "You broke your fucking promise! No one should be in Beckendorf's bed!"
"I'm sorry Luce, I didn't know where else to put him," Jake replied.
Lucifer hissed back, "You could have put him anywhere but Beckendorf's bed!" There was the faint sound of cracking in her voice. "You know, fuck you, apperantly I can't trust you. So don't expect any help any time soon." A few seconds later the door slammed shut and he heard Jake cuss. Leo just shrugged it off and fell asleep again.

Leo knew he should probably check on Lucifer, so he asked Christopher who's daughter she was. "Hades, but I wouldn't look for her if I were you, she's particually pissed at you," Chris told him.
"Thanks, I'll be back at the cabin tonight," Leo told him.
"Your funeral," Travis told him as he passed by. Leo ignored them and took off towards the cabins.
Hades cabin was, slightly terrifying. Not like the Ares cabin though. The Ares cabin looked like it tried too hard to be terrifying, while Hades' cabin, just was. It was like Drew compared to Piper, Drew tried too hard to look good (even though she was Aphrodite's daughter) while Piper just did. The soild black walls were only broken by the two torches burning green fire and a skull (which was chipped in places). Leo slid open the door, slipping in before shutting it again. There was a faint sound of tapping echoing in the cabin, a black haired girl curled up in a ball on the floor besides one of the beds.
The sound was reverbrating through the Hades cabin: .-.-.-...-... Leo knew what she was saying. Worthless. And repeating it, over and over. "You ok Lucifer?" Leo asked quietly, making the girl's head snap up and jump to her feet. There were faint tear streaks down her face.
"You're the kid who took Jake's place," she asked, but it was more like a statement. Leo nodded. "Get out."
"At least tell me why you hate me," Leo requested.
Lucifer breathed out, not understanding the sudden posession where she spilled out her feelings. "I'm afraid if they forget Beckendorf, th-they'll f-forget me. I-I'll just-t be t-the emo da-daughter of H-Hades, n-no one sees-s," she managed to croak out, nearly folding in on herself and falling to the floor. But she held strong and held her ground, barely. "I-I spe-spent all my c-camp life in L-L-Luke's shadow, a-after he d-died p-people thought I-I was going to be ju-just like him."

I'm not gonna be my brother, not matter what they think.

"Now I have t-to climb o-out of his shadow again, be-because Beckendorf w-was the o-only one w-w-who didn't-t see me like t-that. He's t-the o-only rea-s-son the He-Hephaestus ca-abin s-tands up for me." She was at the verge hiccups at that point.
"I-I o-only s-stay al-live for Ni-Nico, be-because he's a-all H-ades would ha-have left. And people s-ee hi-m li-ke th-they see me, a de-demi-ga-god wit-th da-daddy is-ssues wh-o'll le-et something t-take him over so-o they c-can t-try to destroy Oly-lympus," Now she was hiccupping, shaking, tears streaking down her face. Leo managed to catch her before she collapsed and started sobbing uncontrollably. "I-I co-coulda sa-save L-L-uke, b-b-ut I-I di-didn't." Persophone's words rang clear as a bell in her head, as violent as cruel as the bitch herself.

You could have stopped him, you could have prevented this whole war, but you didn't try hard enough to stop him.

"I-I'm s-s-sorry I-I-I'm-m-m d-dum-m-mp-p-ping-g-g th-th-this on ya-ya-you, s-sin-c-ce I-I don't-t-t kn-n-now you. I-I ju-just, I-I f-fuc-k-k everyth-thing up. I-I have to p-rove myself t-t-to peopl-e-e that wo-won't c-care." She buried her face in the crook of Leo's neck, holding on to him like he was the only thing there, only person who mattered.

He's not, Beckendorf was, now this kid is taking that from him.

Years of running got her this, curled up in some guys lap bawling and telling him what no one else knew. Leo wrapped his arms around her, keeping her together, the way no one else could. He stared at the wall he was facing, seeing his reflection in the broken obsidian, his arms wrapped around Hades' daughter. Slowly the broken wall started to fix itself, cracks disappearing slowly.
He picked her up and laid her down on the nearest bunk. She wouldn't stop clinging to him, so Leo slid onto the bed next to her, wrapping his arms around her while pulling the blanket over them. Leo was afraid he'd break her, with how broken she already looked. Her skin was losing some of its ruddiness, making her look haggard and frail, like a sick child. She was curled up on herself, huddled next to him, looking like a terrified little kid.
She reminded him of, him, though she was older than him. Holing everything up until one thing just cracks the dam and can't keep it any longer. It killed, keeping everything bottled up and just taking off when someone got too close. When a place became too much like home.
She finally stopped crying, but still held onto him with a tight grip. She still had a good four inches on him, so it was a little awkward as she buried her head in his chest. "Th-th-thanks," she stuttered, his shirt muffling her voice. "S-sorry for be-being s-such an ass before."
"It's okay," Leo whispered in her black hair.

Lucifer looked at herself in the obsidian, lining her eyes with heavy black eyeliner. One was raven black, like they usually were, but the other was blue, like Luke's had been. One half of both families.
After Luke left, she kept her face hidden, or at least the half with the pale scar running across her cheekbone. Annabeth would look at her and Lucifer knew she was going to say "Luke" but caught herself when she noticed the black eyes and the black hair. Lucifer didn't want to be seen as Luke, so she hid as much as she could, wearing black instead of the camp clothes, keeping her eyes black, growing her bangs out that they covered her face, but the thing she couldn't change was sword fighting. Everyone said with her fighting style mixed with how she fought with a sword, she'd be able to take Luke down, easy.
She pulled her hair back in a ponytail, only a small portion fell in her face, and it was because it would be awkward if she didn't have it hanging in her face. Lucifer pulled her Celtic's jersey (which was equivalent to Greek armor, but was as light as a regular jersey would be) Hermes' had given to her at Luke's funeral. Then she slid a black hoodie on, her sword, Cerberus, which Jake, with Zeus and Hades' permission of course, was reforged, using the remains of Backbiter and Lucifer's broken Stygian iron sword, was tucked safely into a hidden pocket it as a Sharpie (everyone, demigod and god alike, thought it would be better to make sure the blade was only out when absolutely needed) and her back up double Stygian iron swords in their scabbards on her back. Lucifer shut the door to Hades' cabin, the green fire burning black for a second as she passed through.
For some reason it did that when she passed through, Nico thought it was her extensive use of dark energy to use black fire. He was probably right, but to truly know she'd have to ask her father.
Hades' daughter took off towards Bunker nine, barely touching the soggy ground as she ran. It was still cold from the winter, but gradually getting warmer, especially with Camp Half-Blood's magic boundaries.
Soon she was entering Bunker Nine, which still managed to awe her every time she stepped inside. The Argo II was coming along well, and all the random side projects sitting on work benches made it look even more amazing. Outside of the Hephestus cabin she was the only one who really appericated the beauty of machines.
The person she was looking for was at his bench, leaning against it. Lucifer walked over to him, her eyes scanning over the random machines, telling who had created what. "Lee la mañana," Lucifer told her boyfriend.
Leo looked up at her, smiling tiredly, "Mañana." He had grease smudged across his face, his brown eyes bright against the soft glow of the lights. He couldn't have looked any better. Leo reached for a rag, attempting to get some of the grease off, only rubbing more on his face and hands. Lucifer laughed, "La grasa es una buena mirada en usted."
Leo blushed under all the grime. She was the only one that could make him do that anymore, not when he was embarrassed because he thought he had messed up something.
They had fixed each other over the last couple months, since that night Lucifer broke apart in front of him. Lucifer was no longer in Luke's shadow, and Leo didn't think he was inferior, to anyone, he didn't try to prove himself when he defiantly did not need to.
"La noche?" Lucifer asked.
Leo nodded, threading his arms around her waist, "Sí."
"Me podrí haber quedado y le ayudó," she replied as he pressed his lips to hers. It was pure bliss every time he kissed her, sending a pleasant feeling of warmth through her body.
"Usted necestia el sueño," he told her before kissing her again.
The fire in the lantren (because Leo is Leo) was flickering black and blue, a result of the two pyros' emotions mixing. "Por favor, no me obliques a arrastrar el culo a la cabina de Hades y abrazarte hasta que se duerme," she begged.
A smirk danced across his lips, "Promesa?"
Lucifer laughed, "Pervertir."
"I know," Leo told her, pressing another kiss to her cheek before letting her go and cleaning up. "I'm guessing you're dragging me to breakfast?"
"Etiam," Lucifer replied, taking his hand and pulling him away from his workbench. "You need to eat, the Argo II is further ahead than we planned, so don't work yourself to death. If you do who would I have to make out with?"
"Connor Stoll seems to have his eyes on you," Leo joked.
Lucifer made a face as they walked, fingers intertwined, "Sorry, in a way he is my brother, so óchi. But seriously, you need to take care of yourself, I can't lose you too." Leo could see the sadness in her eyes. He couldn't tell if it was the thought of losing him, or thinking of Beckendorf. It's not like he meant to skip meals and sleep, but a lot was riding on this, he wanted it perfect.
"You won't Luce, I promise," Leo whispered, wrapping his arm around her shoulders and keeping her close as they walked.
Lucifer sat down next to Leo at breakfast, dropping a bag of M&Ms she'd gotten from the Hermes cabin on his tray. Sure she should be sitting at the Hades table, but since January she'd been skipping from the Hades to Hephaestus to Hermes table, really only sitting at her table when Nico dropped in for a stay. She'd also taken Nico's position as Cabin 13's head counselor meaning her and Leo spent even more time together. Even the Aphrodite kids were starting to get disgusted with them together.
"Hephestus counselor and Hades' daughter, not the counselor we were expecting but..." Connor started, shoving between Lucifer and Leo while stealing some food from them. He realized the sudden foot wedged in mouth moment. "I couldn't ask for a better soon-to-be step-brother-in-law." Both Leo and Lucifer turned bright red, the fire fickering different colors as some campers scraped food into it, making one of the Aphrodite girls yelp in pain. "Wow."
"Hey, hurry Connor before an Apollo kid gets her," Lucifer told him, imitating what someone would sound like talking to a dog. Connor growled at her before disappering to find the injurd Aphrodite girl.
Leo yawned half way through breakfast. "I'ma steal your brother Jake," Lucifer told Leo's brother.
"Ok, but make sure we're not going to have any nephews or nieces within the next ten months," Christopher laughed, making both turn bright red again, and a passing Hermes son slap him over the head, as they got up and went to sacrfice the rest of their breakfast to the gods.
Chiron was waiting to talk to them. "Don't worry, Cerberus is going to be in my cabin with us," Lucifer reassured the centar. Cerberus became a helper at camp, being a decendant of Lupa directly (yep, he's a mutt AND decended from Rome's founders' surrogate mother).
Cerberus sat down next to his friend and nodded. "I'll make sure nothing happens," the dog told Chiron.
"Ok, you three may go," the centaur agreed.
Lucifer pulled Leo to the Hades cabin, shutting the door when Cerberus was inside. She pushed Leo onto her bed, joining him under the black covers while Cerberus curled up at the foot of the bed. Leo wrapped his arms around his girlfriend, who was curled up to him. "I love you," he whispered kissing the top of her head before yawning again.
"I love you too," Lucifer replied. "Now sleep." Leo laughed before falling asleep.