Rikka Takanashi

Kumin tries to understand what Rikka is saying and doing, even though she is not a chuunibyou herself. She also seems to form a particularly close relationship with Rikka, as she enjoys hanging out with them and did her best to keep the club from being shut down, and a mutual trust is shown as Rikka temporarily "handed down", the power of the Wicked Lord Shingan to her. She finds chuunibyou fascinating and fun. 

Yuuta Togashi

Despite Kumin's behavior, Yuuta respects her as an upperclassman.

Makoto Isshiki

She is friendly towards Makoto. Being an airhead, Kumin does not notice Makoto's feelings for her. Kumin was sleeping when Makoto confessed his feelings to her at the school festival, and turned him down. Like most of the rest of the cast, Kumin doesn't even recognize him at times due to his sudden appearance changes. 

Shinka Nibutani

Kumin understands her despite Shinka's behavior and actions. But her airhead behavior annoys Shinka; though Kumin is an upperclassman, her behavior made Shinka comment that Kumin should behave more like a senior.