Team ROT (Reiji, Otoya and Tokiya) all struggle with depression.
Team kawaii (Ai, Syo and Natsuki) all have some sort of identity crisis. Syo's height, Natsuki's dissociative identity disorder, Ai being a robot.
Masato, Ren and Ranmaru (I've forgot what the team is called) all have some sort of family issue. Ranmaru's family debt, Masato's father... you get the jist.
Team Royal (Camus and Cecil) both left behind their countries to please others.