Kazuma Tamura, a seven-year-old boy bursting with energy and athleticism, lives in Moonlight Town with his family: grandfather Tommy, mother Ai, and father Makoto. His mother works part-time at a supermarket and his father is a salaryman, forming a typical modern Japanese household. Kazuma often spends his time engaged in physical activities and outdoor play.

His life changes when he encounters Ojarumaru, a young prince accidentally transported from the Heian era. Kazuma facilitates Ojarumaru's integration into the Tamura home and becomes his guide to contemporary life. He explains modern inventions, social customs, daily routines, school life, local festivals, and common household objects unfamiliar to the displaced noble.

Kazuma regularly joins Ojarumaru on adventures and misadventures throughout Moonlight Town. He accompanies the prince during explorations, interactions with the town's eccentric residents, and playful engagements with local children. Amidst supernatural encounters, such as the recurring pursuits by the Little Oni Trio seeking Enma's scepter, Kazuma often provides a grounding influence.

Kazuma demonstrates consistent kindness and patience, helping Ojarumaru navigate cultural misunderstandings and emotional challenges stemming from his displacement. The Tamura family serves as Ojarumaru's primary support system, with Kazuma actively facilitating his friend's adaptation to their household rhythms and customs. Kazuma's ordinary childhood experiences—attending school, sharing family meals, playing neighborhood games—provide a contrast to Ojarumaru's aristocratic background, forming the backdrop for their shared daily life.

Kazuma's relationship with Ojarumaru evolves into a steadfast friendship characterized by mutual reliance during both mundane activities and extraordinary situations involving time travel or encounters with Heian-era figures. Kazuma remains a stabilizing figure, bridging Ojarumaru's historical origins with contemporary Japanese society through his actions and explanations.