Some spoilers about Risette:3
Spoiler!
She is indeed Fjord sister(same mom, same dad) she was born right before his dad died and was hidden in the countryside. In the past life, she shows up when Fjord die(it was hinted that from s*icide), but it's sooner in this life. She has the power to control dolls and it's her main weapon. She's actually a very pitiful child like the other kids, she loves her mom and try really hard to earn her mother love by trying to harm Lily or kill Fjord to replace him. But in the future Lily'll show her how being loved feels like(but she's still on her mom side cus I think she's scared). She'll rescue Lilyca in the fight with her mom in the very end and ask them to kill her. Idk what happens to her after that but Atil said she's going to be arrested for treason:(