Old Man Hiramatsu is a recurring customer at Magic Shop Leon, the series' primary setting. This elderly man frequently visits the shop and engages in inappropriate conduct towards the female staff, specifically targeting Nova Luminous. His behavior includes physically touching Nova, such as stroking her buttocks, which she silently endures.

His actions occasionally fuel minor comedic situations. Fino Bloodstone's reaction to his presence, declaring she could "take down that old man with a single punch," exemplifies this, showcasing her demonic nature and unfamiliarity with human social norms. The character receives no significant background details, character development, or exploration of his personal history, relationships, or life beyond the store. A standalone OVA story involving a brother and sister does not connect to or expand upon his character.

Across all official media, including spin-offs and additional seasons, Old Man Hiramatsu experiences no substantial narrative arcs, evolution, or expanded background. His role remains strictly confined to brief appearances as a customer whose inappropriate actions primarily serve to generate situational humor and provoke reactions from other characters within the main setting.