A holy beast called Behemoth, the most powerful being in its world, dies and is granted the chance to reincarnate as a human for a certain reason. On the very day of its reincarnation into a new life, it saves an elf maiden from a deadly attack. Grateful for being rescued, the elf makes an unexpected request that same night, asking to have sexual relations. The protagonist soon discovers that this elf is in fact a princess of the realm and is already the fiancee of the kingdom’s hero.

Taking the name Chrono, the reincarnated Behemoth resolves to live as an adventurer in the imperial capital. The story follows Chrono navigating human society while retaining his legendary status and power from his previous life. The central conflict emerges from his entanglement with the elf princess, as he inadvertently becomes romantically involved with the hero's betrothed. The manga blends fantasy and ecchi elements as Chrono contends with the consequences of his actions while adapting to his new human existence.