Yuta&rika are from Jujutsu Kaisen.When Yuta and Erika where young,They both promised to marry each other,however before that could happen rika was hit by a car,Yuta couldnt accept her death so unconsciously accidentally turn her into a Curse spirit,She would protect Yuta by attacking and killing anyone who she thought bothered him,she was basically uncontrollably in tell Yuta was taken in by gojo,And learn to use curse energy,he eventually made peace with rika,now both are helping to stop Sukuna