Mitsuki is a high school student summoned from Japan to another world alongside Akari Tokitō by King Grisarika of the ruling Noblesse class. Summoners assessed his magical ability as "null," concluding he held no valuable powers, and expelled him from the royal castle without support. Stranded and desperate, he encountered Menou, an executioner tasked with eliminating summoned "Lost Ones" to prevent disasters caused by their unstable abilities. Menou revealed that Mitsuki's Pure Concept was not nonexistent but "Nullify," enabling him to nullify or destroy any object or phenomenon he focused on. She deemed this power excessively dangerous, as uncontrolled use could destabilize the world, and executed him moments later to neutralize the threat. His summoning was orchestrated by the subversive group The Fourth, who intended to use him as expendable bait to conceal Akari's presence. Menou later confronted and eliminated members of The Fourth involved in his summoning, holding them accountable for exploiting an innocent person and indirectly causing his death.