Kei Midoriyama is 23 years old and one of the members of the dance group Prism. He's considered the "responsible older brother" of the group, despite not being the eldest. His dance movements are elegant and precise.

In keeping with the group's theme, Kei's color is green, and he dyes his hair green to reflect this. He has green eyes and stands at 5'11". He's fit from a lifetime of dancing. His voice is gentle and soothing. Kei is responsible, hardworking, and diligent.