Tōsuke Iwasaki, an inventor driven to advance Japan's electrical technology, bears a surname meaning "rock cape" (岩崎) and a given name meaning "peach assist" (桃介). His ability to see spirits stems from a traumatic childhood event where he believes a spirit caused his mother's death, fueling his obsessive goal to eradicate all spirits.

In "Hanakagami no Fantasia," Tōsuke specifically seeks vengeance against a snake spirit he blames for his mother's demise. He shatters a mystical flower mirror to trap this spirit, enlisting Mei Ayazuki to gather the scattered fragments. During their quest, he exhibits protectiveness towards Mei, though he dismisses it as unimportant. His interactions with Mei reveal deeper complexities beneath his resolute exterior, especially when he shares details of his past.

At the climax, Tōsuke restores the mirror and uses his electrical device to confront the snake spirit within its realm. Ignoring Mei's intervention, he attacks, resulting in Kyōka Izumi sacrificing himself to shield Mei. As Kyōka lies mortally wounded, the snake spirit reveals a pivotal truth: Tōsuke's actual mother died of illness, and the spirit had merely assumed her form out of care, departing when she could no longer maintain it.

This revelation forces Tōsuke to confront his vendetta. Kyōka's dying words emphasize redemption, prompting Tōsuke to reconcile with the spirit. The snake spirit then sacrifices her own existence to revive Kyōka. Tōsuke makes peace with her before returning to the human world, his character fundamentally shifting from vengeance to acceptance.