Nathan shuffled uncomfortably on his seat as Ajuka probed him with a stick. One that measured his demonic energy.

"Alright, I'm going to drain your energy. Tell me if you feel the third energy source disappearing."

Nathan nodded, before wincing in pain as he felt his energy being sapped.

As a few minutes passed, Nathan only felt more tired, and eventually when he couldn't handle it anymore, he collapsed on his chair.

Ajuka, seeing the imminent signs, caught him as he fell forward, before setting him straight. "Are you okay?"

Nathan replied, "I'm tired, but otherwise I should be fine."

Ajuka nodded, "Good. Anyways, as you can probably tell, the treatment failed."

Nathan nodded. The foreign energy source was still in his body. He felt it.

"Although I was able to drain it to the point of almost disappearing, it still stayed there as an empty vessel. As time pass, it'll recover- similar to your demonic energy."

"Okay."

"Well, that's it for today. You can go now, and come back next week for a check-in. Of course, feel free to stay and help me with my research." Ajuka joked as he wrote down notes on a clipboard.

"Sure. I have nothing to do anyways."

"Good. Help me fine tune the toy that I'm supposed to send to Sirzechs' little sister.", Ajuka pointed at a table without looking up from his notes.

Nathan nodded wordlessly as he walked over to the table that Ajuka pointed at, picking up… a doll.

"What am I supposed to do with this?"

Ajuka replied once again, this time appearing next to Nathan without a word, "Inject demonic energy into it."

Nathan did as Ajuka said, and instantly, the doll underwent a metamorphosis.

It went from being a Victorian-styled doll into a Gundam. The doll's transformation was abrupt, but it was short enough for Nathan to see. The doll's face opened to shift into a robot head, and so did its body.

Nathan whistled as he moved the Gundam around, noting that it had cannons on the side of its arms.

"Can the cannons deal fatal damage?"

"No. At most, they'll be able to give someone a bruise. Of course, there's an exception if someone uses an offensive power… like the Power of Destruction. In that case, it'll probably disintegrate a few patches of skin, but nothing lethal should happen."

"I… see. So what is it that I need to do?"

"Make it so that the doll transforms instantly."

"How do I do that?"

"Figure it out yourself.", Ajuka smiled as he walked away, heading deeper into his laboratory.

Nathan's face twitched as he watched Ajuka walk away, before sighing and covering the doll with his demonic energy to inspect it.

'There's a problem with the joints that allow demonic energy to flow through them… it's not big, but it's still a mistake…', Nathan thought as he examined the doll, and finally, he came to a conclusion. 'The joints are clogged.'

Nathan picked up the doll and prepared to use his demonic energy to flush out the remnant ones inside of the joints, but on second thought, Nathan stopped.

'If I'm not careful enough, I might overload and cause the doll to explode.'

Nathan decided to go with precision, rather than brute force.

'One at a time… slow and steady.'

Nathan slowly flushed his demonic energy through each joint, one at a time, erasing the remnant traces of demonic energy with his own. Or at least, trying.

His brow furrowed with intensity as he realized- this was Ajuka's demonic energy.

'Of course. He's a Super Devil after all.'

Ajuka's demonic energy resisted against his own, pushing back against him with little effort, and Nathan realized that if he wasn't careful, he would be overwhelmed.

'As expected of the strongest Devil…'

Nathan composed his breath as he fought back against the demonic energy, while being careful as to not overload the joint.

Nathan slowly circled the demonic energy with his own, compressing it from all directions, and eventually, he dispersed it.

'That was way harder than it should've been…'

That's one down. Ten more to go.

'I'm going to be here for a while…'

"Have a good day.", Nathan bidded farewell to Ajuka as he left his lab.

"Wait.", That one word caused Nathan to stop in his tracks.

Nathan turned around cluelessly, and he asked with his eyes, 'What more do I need to do?'

Ajuka smiled and handed the doll over to Nathan, "Deliver this to Sirzechs."

"Why me?"

"Why not you? Anyways, this should be a good opportunity to establish a connection with the Sirzechs Lucifer, no?"

"...", Nathan wordlessly accepted the doll and asked, "Where am I supposed to go? His office? Gremory territory?"

Ajuka hummed as he placed a hand on his chin, "Go to the Gremory territory. He should be there for dinner."

"He can do that?", Nathan blurted out, before clarifying, "I thought that Satans weren't allowed to show favor towards their former clan?"

"We aren't.", Ajuka agreed, "But no one really enforces that rule anyways."

"I see… Well, I'll go now. Can you send me over there?"

"Sure."

Ajuka created a teleportation circle underneath Nathan's feet, and a second later, Nathan reappeared at the edge of the Gremory territory.

Nathan looked around for a few seconds, before finding the castle that stuck out like a sore thumb.

Nathan walked in the direction of the castle, and after a few minutes, he arrived at the gates.

Guards were stationed there, as Nathan expected, and Nathan pulled out the doll that Ajuka instructed him to deliver.

"Maou Beelzebub told me to deliver this doll to Maou Lucifer."

The guards glanced at the doll for a moment, before gesturing for Nathan to hand it over to check for any traps.

After finding no problems with it, the guards returned it to Nathan as the other one sent a message to Sirzechs.

"You can go. Someone will receive you at the entrance."

"Thank you."

Nathan continued on his way to the Gremory castle, and as he approached the entrance, he noticed a woman waiting. More specifically, Venelena Gremory.

'Why is she here?', Nathan stared dumbfoundedly at her.

After a few seconds, Nathan snapped out of his stupor and approached her with a nervous smile on his face.

"Hello? I'm here to deliver this doll to Maou Lucifer, at the behest of Maou Beelzebub."

Venelena smiled at him, "I see. Then, let us go to him..", before she beckoned him to follow her.

Nathan hesitantly followed Venelena through the castle, mentally noting the exit routes, before realizing- there was none.

'Of course… with a family like the Gremory's, they're not trapped in here with you- you're trapped in here with them.'

A few minutes went by as they continuously walked through the absurdly large castle, before they arrived in front of a room. Specifically, Rias' room.

Venelena opened the door to Rias' room, and she entered it, before signalling for Nathan to enter as well.

Inside the room, Nathan noted that there were many magic circles, ready to be activated at a moment's notice, and he also saw that Rias and Sirzechs were watching anime together.

As Nathan and Venelena entered the room, Rias and Sirzechs looked up from whatever they were watching- one with a confused expression, and the other with glee.

"Mom? Who is this?", Rias immediately got to the point, standing up and pointing a finger at Nathan.

Nathan looked at Rias, and realized that she was younger than he was. Maybe by 4-5 years.

Venelena simply smiled and said, "A guest. He has something for you."

At that point, Sirzechs stood up and walked over to Nathan, before leaning in and whispering, "Is this the doll?"

Nathan, surprised by Sirzechs' approach, nodded, "Yeah. This is the doll.", before handing it over to Sirzechs.

Sirzechs beamed at Nathan before turning around to Rias, "Ria-chan! This is the thing that I was talking about!"

Rias' attention was on Sirzechs now, specifically the doll in his hand. She had a twinkle in her eye as she said, "This is the doll that you were talking about?"

Sirzechs smiled and activated his demonic energy, channeling it into the doll.

The doll instantly morphed into a Gundam without a second of delay, astonishing Rias and taking her attention.

That was not what Nathan's attention was on. It was on Sirzechs, specifically his demonic energy.

Nathan's throat felt dry as he probed deeper into Sirzechs' demonic energy, feeling the sheer potency and power of it.

'It's just like Ajuka's…'

Sirzechs then handed the doll to Rias, and she beckoned Venelena to come over to her, leaving Sirzechs and Nathan to look at each other.

"You're the boy that Ajuka was talking about, Sekirai?"

Nathan nodded, "Yes, Maou Lucifer."

"Please, call me Sirzechs. That title makes me feel like I'm one of those stuck-up guys in the anime that Rias is watching."

Nathan nodded, and continued the conversation, "What did Maou Beelzebub say about me?"

Sirzechs rubbed his chin and thought, "Well, he said something about you being cursed, and you having a lot of demonic energy for your age."

Nathan nodded. Those things were natural.

"Speaking of your curse, can I check it out?"

"Feel free. It'd be nice if you can get rid of it as well."

Sirzechs laughed, "I'll try."

Sirzechs then walked over to Nathan, and put a hand on his shoulder, before closing his eyes in focus.

Nathan instantly felt a foreign source of demonic energy, and his body wanted to flush it out- just like an immune system, but Nathan suppressed that instinct. If Nathan tried to flush it out, he felt like it'd do more harm to him.

After a few more seconds of uncomfortable silence between the two, Sirzechs opened his eyes and said with a sigh, "I can get rid of it, but there might be unknown effects on your body. It seems like the energy has already fused with a part of your demonic energy."

Nathan closed his eyes and said helplessly, "So it's like a parasite?"

Sirzechs nodded, "That's how I would put it. I'm sorry I can't do more to help."

"It's no problem," Nathan sighed before saying, "If there is nothing else, I will go now."

As he walked out the door of Rias' room, he felt a hand grip his shoulder. He turned back to see Venelena smiling at him.

"Since you came all the way here, why don't you stay for dinner?"

Nathan mentally twitched his mouth, 'I'd rather go back to Greece than stay here any longer… it's too awkward…'

Of course, his mouth did not agree with his brain, "Of course. I'll notify my parents, then."

Venelena smiled, and ushered him and Sirzechs back into Rias' room.

Nathan was sitting on the bed and was out of focus, until he felt a hand tap his legs. He looked down to see Rias, who shyly asked him, "Do you wanna watch anime with me?"

Nathan smiled back, "Sure."

'I can't really deny… because your brother is sitting right next to me.'