"March Comes in Like a Lion" centers on Rei Kiriyama, a 17-year-old professional shogi player who lives alone in Tokyo. Orphaned at a young age, Rei struggles with feelings of isolation and depression, exacerbated by the pressure of his shogi career and the strained relationship with his adoptive family. The series explores his journey toward emotional healing and self-discovery, interweaving themes of family, friendship, and personal growth.

Rei's life begins to change when he meets the Kawamoto sisters—Akari, Hinata, and Momo—who live in a small, warm household in a different part of Tokyo. The sisters, who have also faced their own hardships, offer Rei a sense of belonging and unconditional support. Akari, the eldest, acts as a nurturing figure, while Hinata, the middle sister, shares a deep emotional connection with Rei. Momo, the youngest, brings lightheartedness and innocence to their interactions. Through his growing bond with the Kawamotos, Rei gradually opens up and begins to confront his past and present struggles.

The narrative alternates between Rei's shogi career and his personal life. As a professional player, Rei faces intense competition, self-doubt, and the weight of expectations. The series delves into the intricacies of shogi, portraying it as both a source of Rei's identity and a metaphor for his internal battles. Matches are depicted with tension and psychological depth, highlighting the mental and emotional toll on the players. Rei's relationships with fellow shogi players, including his mentor Harunobu Nikaidou and rival Souya Touji, further shape his growth and understanding of the game.

Parallel to Rei's story, the series explores the lives of the Kawamoto sisters and their own challenges. Hinata, in particular, faces bullying at school, which resonates deeply with Rei due to his own experiences. The series portrays their struggles with sensitivity, emphasizing the importance of empathy and resilience. Through these interconnected narratives, "March Comes in Like a Lion" balances moments of melancholy with warmth and humor, creating a poignant exploration of human connection and perseverance.