According to the Youku video platform, in the anime Detective Conan, Akai Shuuichi once worked undercover in a gang-related organization, during which he met and fell in love with Miyano Akemi.
Miyano Akemi has a younger sister named Haiyuan Ai. In order to protect Haibarai, Akai Shuuichi promised to protect Haibarai like a knight protects a princess. Akai Shuuichi's promise was later widely spread by fans and became the title of "Haiyuan loves Princess".