"Imōto DX" centers around the life of a young man named Kōta, who finds himself in an unusual living situation after his parents move abroad for work, leaving him to care for his younger sister, Akari. Akari, a high school student, is cheerful and energetic but often relies on Kōta for support, creating a dynamic that blends sibling camaraderie with moments of comedic tension. The story explores their daily lives, focusing on the challenges and humorous situations that arise from their cohabitation.

As the narrative progresses, Kōta’s childhood friend, Yūki, re-enters his life. Yūki, who harbors feelings for Kōta, becomes a frequent presence in their household, adding a layer of romantic tension to the story. Her interactions with Akari often lead to playful rivalries, as Akari is protective of her brother and wary of Yūki’s intentions. The series balances lighthearted comedy with subtle emotional undertones, particularly in exploring the evolving relationships between the characters.

Another key character is Rina, a classmate of Akari’s who becomes close to the siblings. Rina’s calm and mature demeanor contrasts with Akari’s exuberance, and her presence introduces new dynamics into the group. The story occasionally delves into themes of family, responsibility, and the complexities of growing up, though it maintains a primarily comedic tone throughout.

The plot is episodic, with each chapter presenting self-contained scenarios that highlight the characters’ personalities and relationships. From school festivals and part-time jobs to misunderstandings and heartfelt moments, the series captures the everyday experiences of its cast while gradually developing their bonds. The interplay between Kōta, Akari, Yūki, and Rina forms the core of the narrative, with each character contributing to the humor and warmth that define the series.