"Midori no Hibi" centers on Seiji Sawamura, a high school delinquent with a reputation for fighting and a notable lack of romantic experience. Despite his tough exterior, Seiji harbors a deep desire for a girlfriend, though his intimidating demeanor often scares potential partners away. One morning, Seiji wakes up to discover that his right hand has been replaced by a miniature girl named Midori Kasugano, a shy and affectionate classmate who has secretly admired him from afar. Midori explains that she transformed into his hand due to a wish she made to be closer to him.

The series explores the challenges and comedic situations that arise from this bizarre predicament. Seiji must navigate daily life with Midori as his right hand, concealing her presence from others while dealing with the practical and emotional implications of their unusual bond. Midori, now physically attached to Seiji, becomes an integral part of his life, offering support, advice, and occasional comic relief as he faces various personal and social dilemmas.

As the story progresses, Seiji’s interactions with Midori lead to personal growth, softening his rough edges and deepening his understanding of relationships. The series also introduces secondary characters, such as Seiji’s childhood friend Ayase Hayami, who harbors her own feelings for him, and Rin Sawamura, Seiji’s younger sister, who adds to the dynamic with her protective and observant nature. The narrative balances humor, romance, and lighthearted drama, often highlighting the absurdity of Seiji and Midori’s situation while exploring themes of love, self-discovery, and human connection.

The plot occasionally delves into more serious moments, particularly as Seiji confronts his insecurities and Midori grapples with her own feelings of inadequacy and longing. Despite the fantastical premise, the series maintains a grounded focus on the emotional development of its characters, culminating in a resolution that addresses their evolving relationship and the consequences of Midori’s transformation. "Midori no Hibi" blends surreal comedy with heartfelt moments, creating a unique and memorable narrative centered on an unconventional romance.