Yn was a pawn of rias gremory and it was doing fine until issie was joined into rias peerage the rest of the orc started forgetting about Yn till rias didn't want him anymore so the orc attack Yn making it look like he died from a fallen angel after rias getting Yn chest after rias and her peerage left Yn alone in the forest but he was saved by a black it turns out it to be a women that had cat like figures after healing him Yn wanted revenge after what happened the women told her that she can train him to get revenge Yn accepted  and after the training he joined vali in his group

Yn after training

Sacred gear rose
Uses his aura to fly,shoot energy attacks,also makes powerful attacks with and transforms

Rose form 1

Rose form 2

Rose form three

Yn x kuroka