"Tsukikage Baby" is a manga series that revolves around the life of Itsuki, a high school student who unexpectedly becomes the guardian of a baby named Tsukikage. The story begins when Itsuki's older sister, who is a single mother, suddenly disappears, leaving Tsukikage in his care. Despite his initial reluctance and lack of experience with childcare, Itsuki gradually adapts to his new role, balancing the responsibilities of raising a baby with the challenges of being a teenager.

The narrative explores the daily struggles and emotional growth of Itsuki as he navigates the complexities of parenthood. His journey is marked by moments of frustration, tenderness, and self-discovery, as he learns to prioritize Tsukikage's needs while managing his own life. The series delves into themes of responsibility, family bonds, and the sacrifices required to care for a dependent child.

Supporting characters play significant roles in Itsuki's journey. His classmates and friends provide both comic relief and emotional support, often stepping in to help with Tsukikage when Itsuki is overwhelmed. The interactions between Itsuki and these characters highlight the importance of community and the impact of unexpected circumstances on relationships.

As the story progresses, Itsuki's bond with Tsukikage deepens, and he begins to understand the profound connection between caregiver and child. The series also touches on the challenges faced by young parents, societal expectations, and the resilience required to overcome adversity. Through its heartfelt storytelling, "Tsukikage Baby" offers a poignant exploration of the trials and triumphs of unexpected parenthood.