Masayo Irino is Nagomu Irino's grandmother and Heigo Irino's mother, representing the older generation of the Irino family. She is intrinsically tied to Ryokushō, the family's longstanding wagashi confectionery shop in Kyoto, embodying its traditional values and inherited knowledge.

During a specific Kyoto visit, she actively guides Nagomu's development by personally training him in the shop's required skills and disciplines. Her direct, traditional approach prioritizes hands-on learning and endurance, serving as a significant show of confidence in his potential to uphold the family legacy—directly contrasting with Heigo's persistent disapproval.

At a local festival, Nagomu perceives a vision of his deceased grandfather, Ikkō Irino, standing beside her. Whether supernatural or subconscious, this moment narratively connects Masayo to themes of ancestral support and continuity, reinforcing familial encouragement in Nagomu's journey toward self-assurance about Ryokushō's future.

Masayo's character remains stable across her brief involvement, functioning as a stabilizing figure who bridges past and present through her traditional values and mentorship. Her limited role highlights intergenerational dynamics and the tacit passing of legacy within the Irino family.