Information on the character Hagi from the anime How I Attended an All-Guy's Mixer is limited. He is one of three male university students, alongside his friends Tokiwa and Asagi, who attend a mixer. To their surprise, the women they meet, Suo, Fuji, and Kohaku, are all dressed in male drag because they work at a cross-dressing bar. Hagi is sometimes described as the "plain one" of the group, suggesting he has a more normal or understated appearance compared to his friends. He is the counterpart to Kohaku, the most bashful and reserved of the women.

Hagi's role in the story involves navigating the awkward and confusing situations created by the mixer and its aftermath. He expresses a desire for more attention from Kohaku, insisting that it should be his turn to interact with her. A key moment in his development is his reaction to an indirect kiss with Kohaku, which causes his heart to race and creates a personal crisis as he processes his feelings. This event demonstrates his growing and confusing attraction to her, despite the unconventional circumstances.

In terms of personality, Hagi can be forthcoming about his frustrations. When he feels his connection with Kohaku is not progressing, he voices his discontent directly. He is also shown to be considerate, as seen when he offers his jacket to a soaking wet Kohaku to help her cover up. Other interactions include a scene where he tries to win a fluffy toy for Kohaku at a crane game. His background, motivations, other abilities, and overall development are not detailed in the available information.