Najimi Tenkuuji attends Kyuugetsu Academy as a classmate and childhood friend of Kakeru Daichi, distinguished by the blue antenna-like hair strand atop her head that physically shifts with her emotional state. Heiress to the affluent Tenkuuji Group, her gentle and easy-going demeanor frequently dissolves into vivid daydreams that warp her perception of reality. She nurtures deep-seated romantic feelings for Kakeru, rooted in his rescue of her from kidnappers during their youth.

Consuming carbonated drinks triggers a drunken-like reaction that compels her to disrobe, while intense jealousy—particularly involving Kakeru’s interactions with other girls—transforms her appearance into a Kuribo-like creature from the Super Mario series, provoking her to kick his calves.

Amidst conflicts with anthropomorphic soda cans called Akikans, Najimi purchases a sports drink at Yurika Kochikaze's birthday party, becoming owner to its aluminum Akikan, Yell. She shares a protective bond with Yell, though the Akikan’s fierce loyalty manifests in violent outbursts when Kakeru’s careless remarks upset Najimi.

Her interactions are complicated by classmate Yurika Kochikaze, who proclaims herself Najimi’s lover and fuels rivalries with both Kakeru and Yell. Despite this, Najimi’s focus remains steadfastly on Kakeru, who habitually responds to her affections with obliviousness or comical dismissal.