"Midori's Days" centers around Seiji Sawamura, a high school student known for his intimidating appearance and reputation as a delinquent. Despite his fearsome exterior, Seiji is a kind-hearted individual who struggles with loneliness due to others' misconceptions about him. His life takes an unexpected turn when Midori Kasugano, a cheerful and petite classmate, confesses her feelings for him. Initially hesitant, Seiji eventually reciprocates her affection, and the two begin a relationship.

The story takes a surreal twist when Midori is involved in a tragic accident, leaving her in a coma. In a bizarre turn of events, Midori's consciousness manifests in Seiji's right hand, transforming it into a miniature version of herself. This anthropomorphic hand, referred to as "Handori," retains Midori's personality and memories, creating a unique dynamic between her and Seiji. Despite the unusual circumstances, Seiji remains devoted to Midori and continues to care for her in this new form.

As the narrative progresses, Seiji navigates the challenges of his daily life while adapting to the presence of Handori. The series explores themes of love, loyalty, and perseverance, as Seiji remains committed to Midori despite the physical and emotional obstacles they face. The relationship between Seiji and Handori evolves, blending moments of humor, tenderness, and occasional awkwardness as they adjust to their unconventional situation.

Supporting characters, such as Seiji's friends and family, add depth to the story, providing both comedic relief and emotional support. The series balances lighthearted moments with poignant reflections on the nature of love and the lengths to which individuals will go to stay connected with those they care about. Through its unique premise and heartfelt storytelling, "Midori's Days" offers a distinctive take on romance and the enduring power of human connection.