"Oh! My Girl" is a manga series that revolves around the life of Junpei Nagase, a 25-year-old aspiring manga artist struggling to make ends meet. His mundane routine takes an unexpected turn when he is suddenly entrusted with the care of his five-year-old half-sister, Suzume, after their estranged father disappears. Junpei, who has no experience with children, finds himself thrust into the role of a guardian, balancing his career aspirations with the responsibilities of raising a young child.

The narrative explores the challenges Junpei faces as he navigates his new life. Suzume, despite her young age, is precocious and often displays a maturity beyond her years, which both helps and complicates their relationship. The story delves into their evolving bond, highlighting moments of humor, frustration, and tenderness as Junpei learns to prioritize Suzume’s needs while pursuing his dreams. The dynamic between the two characters is central to the series, with Suzume often providing emotional support and perspective to her older brother.

Secondary characters, such as Junpei’s editor and friends, add depth to the story, offering both comedic relief and moments of insight. The series also touches on themes of family, responsibility, and personal growth, as Junpei gradually matures and adapts to his new role. The challenges of single parenthood, financial struggles, and the pressures of the creative industry are portrayed with a blend of realism and lightheartedness, making the narrative relatable yet engaging.

The plot progresses through a series of episodic yet interconnected events, showcasing the everyday struggles and triumphs of Junpei and Suzume’s life together. The manga balances heartfelt moments with comedic situations, creating a narrative that is both touching and entertaining. Through its exploration of familial bonds and personal development, "Oh! My Girl" presents a compelling story that resonates with readers.