Researcher Muzuki Kishin is developing a drug that turns humans into biological weapons, advancing his conspiracy to dominate the world. His former research partner, Shirasagi Kimberly Hideo, now works as a teacher. Her goal is to develop the Stallion Suit, a device designed to enhance human abilities. She outfits the righteous young girl, Seika Shido, with the suit and appoints her as a fighter to confront and stop Kishin's ambitions. However, transforming into Stallion requires precise English pronunciation to input a voice recognition code. Can Seika overcome this challenge, successfully transform, and stand against the evil plot? And will the outcome lead to an even harsher BAD END than expected?