Rei is a prominent character in the anime series 'Hokuto no Ken,' also known as 'Fist of the North Star.' As a master of the Nanto Suichoken (South Dipper Waterfowl Fist) martial art, Rei is known for his graceful yet lethal fighting style. He initially appears as a mysterious and skilled fighter who is searching for his kidnapped sister, Airi. Throughout the series, he becomes a close ally of the protagonist, Kenshiro, and plays a crucial role in battling against various antagonists. Rei's dedication and tragic backstory add depth to his character, making him a fan favorite.