Academic Status: Previous is 1st year, Class 1. Actually is 2nd year, Class 1.

School: Hakoniwa Academy. Previously is Hakobune Middle School.

Age: 15-16 (Zodiac: Leo)

Blood Type: AB

Mentality:: Zero. Previous is Normal.

Affiliation: Zenkichi's Student Council. Previous is Medaka's Student Council and True Flask Plan

Position: President. Previous is General Affairs Manager 

The male protagonist, childhood friend of Medaka, and the Student Council General Affairs Manager, reluctantly joining for the sake of protecting Medaka; in the pilot chapter, Medaka assigns him to become the Vice President. Zenkichi always shows enthusiasm toward Medaka’s cause for helping others and will punish anyone who opposes that cause. It is later revealed that he is the one who reformed Medaka into her current personality. It is implied he has feelings for her. Little is known about Zenkichi's past except that he has been with Medaka since they were two years old. The relationship between Shiranui and Zenkichi is frequently commented on by their classmates, often negatively, on how they interact with each other. Shiranui has commented that she is only friends with him when she is in the mood. Ironically, Shiranui's grandfather notes that Zenkichi is probably the only person who can get along with Shiranui. Zenkichi eventually reveals his feelings directly to Medaka before sacrificing himself to destroy Kumagawa.