Ms. Y is one of the main antagonists from Streets of Rage 4.
Ms. Y is Mr. X's daughter, and Mr. Y's twin sister. She and her brother took over the Syndicate Crime Organization after their father's death, seeking to rebuild Mr. X's criminal empire. After doing secret experiments the two created a device to mind control people and began organizing the new Y Syndicate to take over Wood Oak City.
She first appears in the cutscene after the 9th stage after the heroes save Max Thunder from her mind control. She attempts to brainwash the heroes but they're saved by Estel Aguirre, who crashes their sound device. Along with her brother, she escapes the place in a helicopter.
She travels to Y Island, where she awaits the heroes in the throne room of the castle there. She engages the heroes in combat, showing off her skillful swordplay, but flees when the tide turns against her. She goes to the roof, where her brother is waiting, and the two of them team up for a last stand against the heroes. In the end, they are defeated, and both are arrested by Adam Hunter.
Ms. Y is first fought in the final stage as the game's penultimate boss. She fights with a rapier, using it for quick short-range stabs, a grabbing move where she jumps behind the player and stabs it in the back, and a dashing thrust with lightning after powering up. Despite being a late boss she is relatively easy since she gets no invincibility during her attacks.
She has fought again shortly after, in a dual boss fight with her brother. Once either of them loses 30% of health, that twin will jump in the background and return in the Y Mecha for the final boss fight. In the patch update after losing 70% of health the twin will jump in the Y Mecha and that twin will regain all of his/her health. If the twin in Y Mecha is defeated first, the second twin will jump into the mecha to continue the fight.