Sakuya Otsuki is the son of a legendary detective, following in his father's footsteps with his assistant, Lilithea. However, something's different about this high-school sleuth. Wherever he goes, he always manages to get himself entangled in his cases—as a murder victim. When Sakuya is tasked to infiltrate a luxury cruise ship, he finds himself killed once again. But every time he reopens his eyes, Lilithea is there by his side, ready to help him get to the bottom of the mystery…

平凡的少年佐藤一直对青梅竹马的小姬有爱意。某天终于鼓起勇气告白，结束后，小姬告诉佐藤，她必须穿越到遥远的地方。佐藤忍不住追随了她的脚步，自此踏上了异世界之旅。小姬是异世界的五个“戒指公主”之一。佐藤突然被小姬求婚，并作为勇者“戒王”对抗充满威胁的世界。而且为了激发戒指的真正力量，他还需要与四公主联姻。与五个公主一起的异世界新婚幻想，就此开始——