Jouji Nezu, almost always called by his nickname Joe, is one of the five first-year male students at Hachimitsu Academy. He is the shortest and most physically frail of the group, with a gaunt and weak constitution. His most distinctive feature is the hood he perpetually wears, which is a detached accessory that he can pair with any outfit, including his school uniform or a swimsuit. This hood casts the majority of his face in deep shadow, adding to his gloomy and mysterious appearance.

Joe struggles with severe stomatitis, a condition that causes frequent mouth ulcers and bloody coughing fits that often interrupt his speech. Although this condition is not physically debilitating, it is a constant part of his daily life and contributes to his sullen and quiet demeanor. Despite being the most introverted and odd member of the group, Joe is surprisingly one of the more lecherous boys, often expressing his thoughts through crass jokes and sarcastic remarks. Another of his defining quirks is a deep and genuine love for ants. He keeps an ant farm, names each individual ant, and claims he can tell them apart despite their identical appearance.

Within the narrative, Joe initially serves as a background member of the group of imprisoned boys. He is generally accepting and supportive of his friends but can be emotionally distant. His role becomes more significant after a key event in which the Underground Student Council president Mari Kurihara’s crow attacks his beloved ants. Enraged, Joe attempts to assault Mari, but is stopped by his fellow prisoner Kiyoshi Fujino, who takes the punishment in his place. This act of sacrifice earns Joe’s loyalty, and he becomes more forgiving and friendly toward Kiyoshi, even defending him against other boys who had ostracized him.

Joe later plays a critical role in the boys’ plan to avoid expulsion by participating in a complex triple-switch disguise to help his friend Gakuto escape from the prison block. Following the group’s release, Joe enters a deep depressive phase. Feeling left behind as his friends become romantically involved, he becomes socially withdrawn and even contemplates getting himself re-imprisoned. He hits a low point where he considers committing a serious offense to return to the prison but is snapped out of his spiral by a small act of kindness from a quiet classmate named Satou, who offers him a cupcake. Satou becomes his primary love interest, and his affection for her helps him find a renewed sense of purpose. Out of awkwardness, he refers to her with whimsical nicknames like Cake-san.

Joe’s key relationships are central to his development. He has been friends with Takehito "Gakuto" Morokuzu since middle school, and the two share a long-standing bond, though Joe often jokes at Gakuto's expense. He is closest with Shingo Wakamoto, as their blunt and laid-back personalities complement each other. Later in the story, Joe becomes unexpectedly involved with the eccentric Mitsuko Yokoyama, helping her create yaoi doujinshi featuring himself and Gakuto. This experience leads him down a confusing path where he briefly questions his own feelings before ultimately recommitting to his role as a supportive friend. Despite his gloomy exterior and initial reluctance to cooperate due to a fear of betrayal, Joe proves to be a loyal friend who offers his support when it matters most. His notable abilities are not physical but rather his surprising strategic usefulness in disguise plans and his unique, if odd, perspective on the world around him.