Hmmm

I think mo dao zu shi could work

I can only think of some where one man is the father of the child or like a nephew
- Our Sunny Days
- Hinadori wa Shiokaze ni Madoromu
- Sensei wa Butchozura Shite Yatte Kuru
- Sekai wa Shippo de Dekiteiru (this 1 is actually adoption)
- Bokura no Shokutaku
- Kazoku Ni Narouyo (sort of like adoption, they mostly take care of the child)
- Boku no Papa to Papa no Hanashi (this is the gold you wanna read. Gay marriage is legalised in Japan and now these 2 can and do adopt a baby. It’s so cute, wish there were more stories like this)

If I Don't Become the Main Character, I'll Die. It's a novel and there's a found family trope. I'm not sure if they actually ended up as a legal family but it's close.

This was some gold! Boku no Papa to Papa no Hanashi Mhmmm

Thank you guys so much! I read too much sweet stuff and I need to go read something toxic now. My teeth hurt.