"T&A Teacher" centers around a young man named Kouta Takamiya, who finds himself in an unusual predicament when he is hired as a substitute teacher at an all-girls high school. Kouta is initially overwhelmed by the responsibility and the chaotic environment, but his situation becomes even more complicated due to the presence of two female teachers, Aoi Hidaka and Risa Kamizuki, who take a keen interest in him. Both women are strikingly attractive and possess strong, contrasting personalities, which often leads to comedic and awkward situations.

Aoi Hidaka is a strict, no-nonsense teacher who values discipline and order, while Risa Kamizuki is more carefree and flirtatious, often teasing Kouta and creating tension between the three. The series explores the dynamic between Kouta and these two women, as well as his interactions with the students, who are equally mischievous and unpredictable. The narrative frequently delves into humorous and risqué scenarios, driven by misunderstandings and the characters' clashing personalities.

Throughout the series, Kouta struggles to maintain his professionalism while navigating the challenges of his new role. The plot often revolves around his attempts to balance his duties as a teacher with the chaotic and often absurd situations he finds himself in, many of which are exacerbated by Aoi and Risa's antics. The series blends comedy, romance, and slice-of-life elements, with a focus on the humorous and sometimes awkward interactions between the characters. The tone remains lighthearted, with occasional moments of character development and introspection, particularly as Kouta grows more accustomed to his role and the people around him.