Kei Yuki drives romantic conflicts as a central figure, engaged to Miss Ayumi through an arranged marriage orchestrated by Hikaru Daitokuji of the Daitokuji financial group. This engagement ignites fierce rivalry between A-ko and B-ko, both pursuing Kei despite his union.

His background includes nearly colliding with C-ko on his motorcycle, retaining an earring she dropped during the incident. Later, he encounters A-ko at her fast-food part-time job, offering her a ride to meet C-ko, who openly dislikes him.

Kei displays minimal agency, characterized as "strangely passive" amid escalating conflicts. He functions primarily as an object of desire, showing disinterest in romantic attention. His engagement proceeds without his input, and he becomes entangled in A-ko and B-ko's violent disruption of the wedding ceremony.

The wedding occurs at Graviton City High School for Girls' gymnasium, where Kei, Miss Ayumi, and C-ko witness an alien invasion and the protagonists' battle. His favorite film is *Tabidachi - Ami Shusho*.

Visually, Kei is designed as a conventionally attractive bishonen, aligning with his romantic role. His motorcycle remains a consistent element, reflecting his introductory scene and transportation.