First examine her body, you will find that the cause of death was a knife stab to her back, you will also find the number 25 written blood, presumably by Ami before her death, implying that the traitor was the one responsible for her death. After examining the body Dhena and Pixie eventually return to the room, and have a short conversation before MC(Main Character) and Pixie leave. After that you should interrogate everyone to find the clue.
I cannot tell you the whole part as it will spoil what's coming next!
Satan || TheArcadean's Helping Team