Billy the Beat Fang
Killer Move Type: Boxing Combination
Users: Billy
Rio (most likely)
Though technically not part of the Hero Association, Rio's personal trainer Billy does have his own Killer Move. This is based heavily on his boxing techniques and his ability to deliver hard, fast punches. Since Rio's Killer Move is very similar to Billy's, it's most likely that he taught her the move and adapted it to her smaller, lighter frame, as well as add kicks.

Billy's technique uses a sequence of fast, brutal punches, with the aim of completely overpowering his opponent with brute force. This ends with a powerful uppercut. Normally this would be effective, but Ratman was able to roll with the punches and his bio-armor was able to withstand the hits. Billy was quite shocked to see that his best technique was not able to stop his opponent.