Kazuichi and Mahiru both are members of Class-77B, and participants of the Killing School trip.
The two interact during chapter one, during which Kazuichi fails to show up to the Ultimate Imposter's meeting at the diner, and Mahiru is sent to find him. After successfully dragging him back, the students were able to begin their meeting.
For a number of reasons, Mahiru finds Kazuichi rather annoying and unreliable, being disgruntled by the need to physically drag him to the meeting in chapter one. In her free-time events with Hajime, she complains about Souda's failure to wash his own jumpsuit. In their official relationship chart, Mahiru expresses that she wonders if Souda has any tact at all.
In the official manga, Super Danganronpa 2: Kazuichi Souda in the Middle of Despair-Inducing Casuality, Mahiru finds Souda again after dragging him to the diner. She berates him further for failing to wash his jumpsuit, but offers to sew a tear in his jumpsuit for him. When Souda informs her that he knows how sew from watching his parents, she seems fairly surprised, but pleasantly so.
It is said elsewhere in this manga that Kazuichi holds a fair amount of respect for Mahiru, and finds her very capable.
Mahiru became the second victim of the Killing School Trip, however, cutting any potential interactions between the two short.
FREE TIME EVENTS
- “That idiot Kazuichi was saying he's never once washed his jumpsuit...”
- — Mahiru about Kazuichi during her third Free Time Event with Hajime.
The ship sailed as a result of Souda and Mahiru's interactions throughout the game, only fueled by their relationship in the manga. Some speculated that the two could work well together, as Mahiru was pleasantly surprised at some of Souda's useful quirks, as well as Kazuichi's implied respect for the girl.
However, some also felt that Mahiru would find Kazuichi's useless as a turn-off to any romantic chemistry, and the ship remains a rare pair amongst the fandom, made rarer still by the fact that their interactions existed in a spin-off manga without full English translation.
- Kazuichi was the third person to discover Mahiru's corpse in chapter two.