"Imōto Paradise!" centers around the life of a young man named Kōichi, who finds himself living with his younger sister, Yūko, after their parents move abroad for work. The series explores their daily lives and the challenges they face as they navigate their sibling relationship in a shared household. Kōichi is a responsible and caring older brother, while Yūko is cheerful and occasionally mischievous, creating a dynamic that balances moments of humor and heartfelt interactions.

The narrative delves into the complexities of their bond, highlighting how they support each other through various personal and academic struggles. Kōichi often takes on a protective role, ensuring Yūko’s well-being, while Yūko, in turn, helps Kōichi lighten up and enjoy life beyond his responsibilities. Their interactions are punctuated by lighthearted moments, such as Yūko’s playful teasing and Kōichi’s attempts to maintain order in their home.

As the story progresses, the series introduces additional characters, including friends and classmates, who add depth to the narrative. These characters often bring new perspectives and challenges, further developing the central themes of family, responsibility, and growing up. The plot remains grounded in the everyday experiences of the siblings, avoiding overly dramatic or fantastical elements, and instead focusing on relatable, slice-of-life scenarios.

The tone of "Imōto Paradise!" is warm and wholesome, emphasizing the importance of familial bonds and mutual understanding. While the series occasionally touches on themes of adolescence and personal growth, it maintains a light and accessible approach, making it suitable for a wide audience. The characters’ development is gradual, reflecting their evolving relationship and individual maturity over time. Overall, the series offers a heartfelt portrayal of sibling life, blending humor, warmth, and relatable moments.