"Tenshi na Konamaiki" centers on Megumi Amatsuka, a mischievous and self-centered middle school student who often uses her charm and cunning to manipulate others for personal gain. Her life takes an unexpected turn when she angers a celestial being, resulting in a curse that transforms her into a boy whenever she is splashed with cold water. The curse reverts her back to her original form when exposed to hot water, creating a series of comedic and chaotic situations as she navigates her dual identity.

The narrative explores Megumi's attempts to adapt to her new reality while maintaining her social standing and relationships. Her transformation complicates her interactions with classmates, particularly her childhood friend, Keiichi Kurimoto, who harbors feelings for her but is unaware of her condition. Megumi's rival, the kind and popular Mitsuki Saito, also becomes entangled in the situation, adding layers of romantic tension and rivalry. The series balances humor with moments of introspection as Megumi gradually learns to confront her flaws and develop empathy for others.

Throughout the story, Megumi's transformations serve as a catalyst for both comedic misunderstandings and personal growth. The curse forces her to experience life from a male perspective, challenging her preconceived notions about gender and relationships. The series incorporates elements of slapstick comedy, school life, and light romance, with a focus on the dynamics between its central characters. Megumi's journey is marked by her evolving relationships with Keiichi, Mitsuki, and other classmates, as well as her ongoing struggle to break free from the curse while reconciling with her own identity.