Responses
Also just realized that in order for Jiu to adopt Yui the biological father need to gave permission and all custody, he ran away cause his situation is hard but Imagine Yui losing her mother then her father is nowhere to be found, then the father came to take her away from the very person who is there when Yui's alone and confused
Not necessarily. If her mother left him before Yui was born, or if he wasn't put on the birth certificate, then permission from the father wasn't needed as they wouldn't have had his name.
Kaisen and Jiu having mature talk thinking how everyone can make a decision together and prioritizing Yui, and then there's the biological father dropping the bomb behind their back