The character "Vieillard" ("Old Man," referred to as "jiisan" in Japanese sources) appears exclusively in *Mind Game*. A former yakuza member, he has been trapped inside a whale for over thirty years before the protagonists' arrival; he is the father of a senior yakuza member pursuing them.

Swallowed decades earlier, he built an elaborate suspended house above the gastric sea within the whale, utilizing debris to create a self-sufficient existence, demonstrating resourcefulness and resilience in isolation.

Upon encountering Nishi, Myon, and Yan inside the whale, he becomes their mentor. He provides survival knowledge, practical advice, emotional support, and philosophical reflections, facilitating their adaptation. He encourages their personal growth: Yan practices dance and art, Myon resumes swimming, and Nishi develops his manga artistry.

Observing the whale's deteriorating health through rising internal water levels, he prompts the group's escape plan. He contributes engineering expertise to construct a motorized boat from parts of the car that entered with the protagonists. His active participation in modifying the vehicle and navigating the escape route is critical to their exit.

He escapes alongside the protagonists when the whale returns to Osaka. The concluding montage reinforces his integration into the narrative of interconnected lives, emphasizing that his story—like all others—"has never ended," underscoring themes of resilience and perpetual transformation from isolation to renewed engagement.