Tadatomo Ijuuin, nicknamed "Bacchiguu," attends Kanenone Gakuen, an all-boys boarding school in rural, mountainous Japan. He leads a self-appointed quartet including Yuusuke Takasaki, Hikaru Ichibanboshi, and Taizou Tenjin. Bacchiguu possesses a highly energetic and impulsive personality, frequently engaging in perverted antics with Ichibanboshi and Tenjin. This behavior stems from frustration with the school's isolated, female-deprived environment and his desire for a typical youth experience. While overtly sexual, his intentions generally lack malice outside direct sexual pursuits.

Physically, Bacchiguu has short brown hair, black eyes, glasses, and is often described as heavy-set. His initial romantic focus is Chigusa Iino, the youthful-looking school nurse and science teacher with prominent physical attributes who accompanies female students during Kanenone's trial integration. Bacchiguu pursues her persistently. However, his romantic focus shifts unexpectedly during the co-ed trial when he accidentally confesses feelings to Arisa Haruno, a female student initially aligned with Futaba Kutsuki's anti-male sentiment. This unintended confession leads Arisa to develop genuine affection for Bacchiguu, and the pair enter a romantic relationship, marking a shift from comedic pursuits to a sincere romantic subplot.

Bacchiguu's narrative role primarily involves generating comedic situations through exaggerated sexual humor and schemes targeting interactions with the newly arrived female students. His tendency to involve Yuusuke in these antics frequently results in Yuusuke facing unjust consequences. Bacchiguu maintains loyal friendships within his core group, but his actions fuel broader conflict between male and female students, particularly drawing the ire of the man-hating Futaba. Across official media, Bacchiguu evolves from a one-dimensional comic relief figure into a character capable of mutual romantic affection, though his fundamental personality traits remain consistent.