In a powerful kingdom on the brink of political tension, Prince Osamu Dazai is next in line for the throne. With the king aging and nobles growing restless, Dazai is ordered to choose a wife—quickly. But Dazai has never cared for duty… or people. Meanwhile, a notorious underground assassin, Chuuya Nakahara, is sent to infiltrate the palace under the cover of night. His mission? Kill the future king before he can rise. He fails. Caught mid-attempt, Chuuya expects execution. Instead… Dazai does something worse. He keeps him. Stripped of his weapons and pride, Chuuya is forced into servitude as Dazai’s personal attendant—dressing him, assisting him, and constantly staying at his side like some obedient “pet.” But the longer they’re forced together, the more dangerous things become—not because of knives… …but because of feelings. And Dazai still has to marry someone else.