Baran is Touma's (and to a lesser extent, Sanger's) rival. Son Ganlong (Avot Akrav) and his Shin Ryuohki are the rivals for Kusuha/Bullet and their choukijins. For some reason, he resents them. I think it has something to do with how they were chosen (to protect the Earth or to guard Gan Eden?) instead of him. He was also involved in the Choukijin Wars in the past.