Yui has a cheerful and optimistic personality, but is somewhat naive as well. She can be oblivious to many things and doesn't catch onto them so easily, as well as having trouble in making decisions in certain cases. Yui seems to be very determined and strong-willed in the worst scenarios and doesn't mind any mean comments thrown her way by any of the vampires. Despite such situations, she usually responds to all the brothers with kindness. As she goes through the game, she slowly starts to become a masochist (though she denies it). Yui is also a strong believer of God. At first, she does not believe in the existence of vampires but eventually comes to accept them.