Mirei Yajima is a first-year university student who joins the Genshiken club after witnessing Chika Ogiue’s manga poster drawing demonstration. She is one of four new members introduced in the second generation of the club. Like several other members, Yajima is a fujoshi, a female otaku who enjoys yaoi (male-male romance) content. However, she is less open about her interests compared to her more exuberant friend Rika Yoshitake. Yajima has a stocky build, wears glasses, and prefers men’s clothing. She is also a relatively inexperienced manga artist and works as one of Ogiue’s paid assistants, handling tasks such as erasing pencil lines and cleaning up pages.

Yajima’s personality is often described as shy, grumpy, and reserved. She tends to keep to herself and can come across as blunt or irritable, particularly when confronted with situations that make her uncomfortable. A notable source of this discomfort is Kenjiro Hato, a male club member who cross-dresses as a girl. Despite knowing the full circumstances behind Hato’s habits, Yajima has great difficulty accepting his cross-dressing and frequently tells him to stop. This reaction stems partly from her own sudden self-consciousness about her feminine identity after meeting Hato, though she rarely expresses these feelings openly.

Despite her gruff exterior, Yajima respects the feelings of others. She often acts as a grounding presence in the club, quietly reprimanding Yoshitake when the latter pushes too far into people’s personal boundaries. Yajima also harbors secret romantic feelings for Hato, a development that adds complexity to her interactions with him. Throughout the series, her internal conflict regarding Hato’s appearance and her own identity shows a gradual, if subtle, development: while she remains uneasy, she begins to engage more with the club’s activities and its members.

Yajima’s notable abilities lie in her practical assistance for Ogiue’s professional manga work. Though she is not a strong artist herself, her meticulousness in cleanup tasks makes her a reliable assistant. Her role in the story is that of a supporting character who contributes to the club’s dynamics, especially the new generation’s mix of personalities. Her key relationships include a friendship–rivalry dynamic with Yoshitake, a working relationship with Ogiue, and a tense but emotionally charged connection with Hato that forms a subtle subplot.