Yasha and Onihime, also known as Mona and Lisa, are a pair of bosses which appear in Streets of Rage and Streets of Rage 3.
In the original Streets of Rage, they make their first appearance as bosses on stage 5. They are very acrobatic, evasive, and clever at delivering their attacks. In the third game they appear as bosses on Stage 2.
They appear as palette swaps of Blaze, bearing almost the same moves. Despite looking petite, they can deliver some of the most damaging attacks in the game; in the hardest difficulty, a single attack can cost 80% of the player's health. It is very difficult to hit them with regular moves, as they'll constantly do backflips which render them invulnerable whenever the player attempts to approach them. A good strategy is to keep one's back turned, then using a back attack (attack+jump buttons) whenever they approach.
In this game they are given a major overhaul. Instead of looking like Blaze, they appear as acrobats in skintight suits. They still bear many of Blaze's moves, with a few more extra moves like double-team tactics that can knock huge chunks of health off. Unlike their original appearance, they will successfully land and take no damage if tossed. They only appear in Stage 2, in a bar located at a dance club.