The raijin (Raiden in the english translation) sisters are identical twin sisters.
Together they are the co presidents of the female wrestling club.
Rai is the ditzy and kind one of the sisters and the eldest, Rai prefers using holds and grapples to weaken her opponent she wears white. While Rin is the more serious of the sisters and wears black. Den prefers the power moves such as slams to cripple her opponent.
While they may or may not have an interest in Densuke. Both sisters belive that he and Chiharu can teach them much about wrestling after they defeated them in the ring.
Though they are twin sisters they are actually only two of quadruplets. Theyre older twin brothers are Gai and Riki, who are the heads of the athletic federation.