Taizou Tenjin attends Kanenone Gakuen, an all-boys boarding school in rural Japan. He is a member of the "Baka Trio" with Tadatomo "Bacchi-Gū" Ijuuin and Hikaru Ichibanboshi, united by their focus on romantic or sexual pursuits involving female students newly arrived under a trial integration program.

Tenjin possesses an "imouto" (little sister) fetish, expressing a strong desire to care for a girl as a younger sister through protective and nurturing behavior. This fixation centers intensely on Sanae Minami, attracted by her youthful appearance, shyness, and perceived vulnerability due to a chronic illness requiring medication. His ideal scenario involves Sanae seeing him as an older brother, allowing him to sit beside her, smell her scent, and eat rice simultaneously—a behavior linked to a linguistic joke referencing the Japanese word "okazu" (meaning both "meal" and "pornographic material").

To facilitate this, he habitually carries a container of rice prominently labeled "Imouto." He seems largely unaware that his conduct, including staring while eating and attempts to physically sniff Sanae, causes her significant discomfort and fear, leading to her consistent rejection and avoidance. His obsession overrides his rationality; he becomes unhinged or extremely agitated upon perceiving any threat to Sanae's well-being, however minor.

His background, family history, and significant character development remain undocumented across the series, its OVAs, or related media. His role is consistently a source of comedic conflict driven by his unwelcome advances towards Sanae and participation in the Baka Trio's antics.