For you as the player, you get to pick which one will “protect” Yui during the game ( ´_ゝ`).
The Sakamakis think that the Mukamis are after the power of Yui’s blood and decide to protect and watch over her. Upon arrival to school, she runs into 4 new half-vampire transfer students, the Mukami brothers. One day on the way to school, their car has an accident and during the process Yui starts trippin’ balls and seeing Karl Heinz invading her brain telling her she is “Eve”. And so our heroine Komori Yui has been living with her abusive man-harem for some time and they are all fully aware of the power and source of her blood.