Shun Kishida is a transfer student entangled in mysterious occurrences across different eras. Multiple characters encounter him during their youth and later as teenagers, yet he consistently appears unchanged, maintaining the same adolescent form regardless of the time frame, marking him as existing outside conventional time.

He frequently materializes at pivotal moments in others' lives, triggering flashbacks or unexplained phenomena. Tamaki Saimon recalls meeting him during her childhood while also seeing him as a current transfer student. School librarian Fumi Yokomizo remembers interacting with him years earlier during her own time as a student at the same institution. His presence appears documented even in historical media, like an old film discovered during research.

Kishida speaks cryptically about temporal concepts, deepening his enigma. He often stands apart as a silent witness to events rather than directly intervening, though characters initially attribute unexplained rescues or occurrences to him; Tamaki mistakenly believes he saved her from assailants, though Sukekiyo Koudaiji was actually responsible. Paper airplanes and water recur around him, symbolizing transience and memory across timelines.

His background remains deliberately unresolved, the narrative emphasizing unanswered questions about his origins, motives, or connection to recurring future scenes depicting abandoned school grounds. Kishida functions primarily as a narrative device exploring themes of memory and timeless influence, not undergoing conventional development.