Lewin dealing with baby Rin for the first time:

Lewin was no stranger to sleeping through loud things. Even the earth-shattering crying of a baby. What he’s not immune to, is Mephisto poofing into his apartment at an ungodly hour and dumping ice water on him. 

Ice water. His arch nemesis. 

He huffed, trying to seem at least a tad smiley. “Dare I ask what prompts you to wake me?”

“There is a screaming baby in the next room over and you are doing nothing about it.” Mephisto hissed, crossing his arms. Normally, he wouldn’t have cared about a baby’s wellbeing but this was Rin and he really needed this child to survive to his high school years, at the least. “There’s a reason I wanted Shirō to raise the twins. You are not doing a good job.”

“Let me rest!” Lewin cried dramatically and sarcastically. He was already halfway to Rin’s room when Mephisto responded. 

“Not until that baby is taken care of!” 

Lewin grumbled to himself as he looked down at the kid he'd, for some reason, decided to raise. He'd have to train this kid. But he had to raise it first.

He sighed and reached into the cradle. He picked up the baby and it kept crying, squirming in his hold. He frowned. What had he gotten himself into?

He sat in the comfy rocking chair and rocked in it, hoping the methodical movement would lull the baby back to sleep. Rin's cries descended into whines, and then hiccups. He looked up at Lewin with tear stained cheeks and his bottom lip poking out.

"What, are you hungry?" Lewin asked. The baby's thin white tail wagged as a response. Mephisto had left the boy unsealed for freedom and for more power to work with when he'd be training as he grew up.

Lewin got up to go in the kitchen and make the kid some formula.

"Probably gonna have to pick up a book on parenting. Or maybe ask Ma for some tips....." He muttered to himself. He onehamdedly closed the bottle and shook it before offering the nipples to the baby. Rin sucked on it incredibly fast, rapidly draining the bottle. Lewin pulled it from him. "Hey, you gave to drink slow. If you go too fast, you'll throw up, kid." He told the boy. He gave the bottle bank and Rin resumed sucking it down. He pulled the bottle away, again and again, until the baby drank slower.

"That's it, kid." Lightning whispered as he rocked the baby. Rin's features finally smoothed out and he fell into a deep slumber. He snored loudly and Lightning wanted to laugh. How could such a tiny body emit such a loud noise?

Rin would wake up and cry every time Lewin tried to put him back in the crib, so Lewin ended up falling asleep watching late night re-runs of Friends on the couch with the baby snoring and drooling on his chest, kept there by his arm.