Schlain Zagan Analeit, once Shunsuke Yamada, is reborn into a fantasy realm after perishing in a classroom explosion. As the fourth prince of the Analeit Kingdom, his unremarkable past life lingers in his earnest, naive demeanor. Sheltered within the royal castle due to his stepmother’s political maneuvering, he grows isolated from external strife, idolizing his half-brother Julius, the kingdom’s heroic figure. When Julius dies, Schlain inherits the Hero title, thrust into leadership just as a coup orchestrated by his half-brother Cylis and former classmate Hugo exiles him under false treason charges. The mantle of "Ruler of Mercy" intensifies his pacifism, bending his psyche toward nonviolence even when survival demands compromise.

His journey intertwines with reincarnated allies and adversaries: Katia, a childhood friend harboring unrequited love; Sue, his half-sister, whose fixation blurs familial lines; and Fei, a loyal Earth Wyrm companion. Antagonists like Hugo test Schlain’s resolve, forcing him to confront idealism amid betrayal and systemic corruption.

Evolving into a deuteragonist, Schlain clashes with Shiraori (White), who seeks to dismantle the world’s RPG system—a plan requiring mass sacrifice. Driven by prophetic dreams and guided by the benevolent Sariel, Schlain pursues an alternative path, yet his limited grasp of divine schemes and Shiraori’s motives leaves him strategically vulnerable.

Critical battles, such as the Elf Village War, expose Schlain’s tactical inexperience, humbling him into acknowledging his flaws. Despite repeated defeats, his persistence bridges idealism with pragmatic concessions. A final confrontation with Shiraori destroys her physical form but fails to halt her grand design, cementing Schlain’s legacy as a well-meaning yet overmatched figure navigating the fragile intersection of morality and survival.