Cain

A guy that murdered some people for fun who are now haunting him as red ghosts. Yeah not just killed. But murdered. 

Comes from a wealthy aristocratic family and ran away from home after stealing a powerful magic key from there with which he can keep the ghosts of the people he kills by his side

Has always been an irredeemable psychopath who torments others for fun, especially his sister and his family's servants

Actually quite smart but has dumb bitch disease 🙄

Doesn't take anything seriously and just does whatever he wants

Meets Sei in some shady city on a planet far away from his home and doesn't know that their meeting wasn't coincidental at all and Sei was actually hired by Cain's family to bring him and (mainly) the magic key back home

He decides he wants to kill Sei and add him to his ghost collection

They pretend to trust each other (Among us but they're both Impostors)

They then follow Mairi around to "kill some time" all while hiding their ulterior motives ^_^;