Sōmeiji Kawamoto is the grandfather and guardian of Akari, Hinata, and Momo Kawamoto following the deaths of their mother and grandmother and their father's absence. He runs the traditional wagashi shop Mikazuki-dō in Sangatsuchō ("March Town"), where the family lives. Having been orphaned during the war and losing his own family as a child, he understands isolation and survival, shaping his empathy for others facing hardship.

He maintains a calm and friendly demeanor while prioritizing his granddaughters' well-being. He praised Hinata's bravery when she defended a victim of school bullying rather than remaining passive. His protective yet encouraging nature extends to Rei Kiriyama, the orphaned professional shogi player befriended by the family. Sōmeiji identifies with Rei's solitude, gradually developing trust in him and offering subtle guidance and emotional support.

His relationship with Rei evolves significantly. He recognizes Rei's growing bond with Hinata early on and openly encourages their connection, later expressing approval when Rei declares his intention to marry her. Sōmeiji acknowledges this outcome as ideal, reflecting his long-standing hope for their union. He is particularly affectionate towards the youngest sister, Momo, often indulging her.

After losing his wife and daughter, Sōmeiji prioritized his health to avoid leaving his granddaughters alone, overcoming a prior aversion to doctors to manage his blood pressure regularly. His daily life focuses entirely on sustaining Mikazuki-dō and ensuring his family's stability.