"That Cute Kid is Mine and Mine" centers on the lives of two individuals whose paths cross unexpectedly due to a shared connection with a young child. The story begins with Aoi, a reserved and hardworking office employee, who discovers that a child named Haru has been left in his care by an estranged relative. Aoi, unprepared for parenthood, struggles to balance his demanding job with the responsibilities of raising a child. His life takes a turn when he encounters Riku, a cheerful and outgoing kindergarten teacher who becomes deeply involved in Haru’s life. Riku’s natural affinity for children and his warm personality create a stark contrast to Aoi’s more reserved demeanor, leading to a dynamic and evolving relationship between the two adults.

As the narrative progresses, the focus shifts between the challenges of co-parenting and the growing emotional bond between Aoi and Riku. Haru’s presence serves as a catalyst for their relationship, bringing them closer as they navigate the complexities of raising a child together. The story explores themes of family, responsibility, and personal growth, as both Aoi and Riku confront their own insecurities and pasts. Aoi’s initial reluctance to embrace his new role gradually transforms into a genuine commitment to Haru’s well-being, while Riku’s carefree attitude is tempered by a deeper understanding of the responsibilities of parenthood.

The manga balances moments of lighthearted humor with emotional depth, particularly in its portrayal of the evolving dynamics between the three main characters. Aoi’s journey from a solitary, work-focused individual to a devoted guardian is a central arc, complemented by Riku’s unwavering support and Haru’s innocent yet perceptive nature. The series also touches on societal expectations and the challenges faced by non-traditional families, offering a nuanced perspective on modern parenting.

Secondary characters, including Aoi’s colleagues and Riku’s fellow teachers, provide additional layers to the story, offering support and occasional comedic relief. The narrative maintains a steady pace, blending slice-of-life elements with heartfelt moments that highlight the importance of connection and mutual understanding. Through its exploration of familial bonds and personal growth, "That Cute Kid is Mine and Mine" presents a compelling and relatable story that resonates with readers.