"Aishiteru ze Baby" centers around Kippei Katakura, a carefree high school student whose life takes an unexpected turn when he is tasked with caring for his five-year-old cousin, Yuzuyu Sakashita, after her mother passes away. Yuzuyu, who has never met her father, is left in the care of her extended family, and Kippei, despite his initial reluctance, steps up to become her primary guardian. The series explores their evolving relationship as Kippei navigates the challenges of balancing his responsibilities as a caregiver with his personal life, school, and friendships.

Kippei begins the story as a somewhat irresponsible and immature teenager, more interested in flirting with girls and hanging out with friends than taking on serious responsibilities. However, as he spends more time with Yuzuyu, he gradually matures, learning the importance of patience, empathy, and selflessness. Yuzuyu, on the other hand, is a bright and affectionate child who quickly forms a strong bond with Kippei, relying on him for emotional support and guidance. Her innocence and curiosity often lead to heartwarming and humorous moments, contrasting with the more serious themes of loss and family dynamics.

The narrative delves into the struggles of single parenthood and the emotional toll of sudden responsibility, as Kippei faces criticism and skepticism from those around him, including his peers and family members. Despite these challenges, he remains determined to provide Yuzuyu with a stable and loving environment. The series also introduces secondary characters, such as Kippei’s childhood friend, Kotomi Aoki, who becomes a supportive figure in both Kippei and Yuzuyu’s lives, and Kippei’s younger sister, Kokoro, who occasionally helps with Yuzuyu’s care.

Throughout the story, themes of family, love, and personal growth are interwoven, as Kippei and Yuzuyu navigate their new life together. The series balances lighthearted, slice-of-life moments with poignant reflections on the complexities of human relationships, creating a narrative that is both emotionally resonant and relatable. The dynamic between Kippei and Yuzuyu serves as the emotional core of the story, highlighting the transformative power of love and responsibility.