There used to be a boy who could control Youkai with a mysterious watch. However, he became unable to see Youkai when he became an adult. With the boy's duties finished, the watch was buried away in space-time. Then 30 years later, quiet everyday life comes to an end as a fateful day beginning with a comet drawing near. The terrible Youkai virus Onimaro infects people's malevolent intentions and spreads infinitely. The one chosen by the Youkai Watch is the one who can save humanity from its crisis. The bond between humans and Youkai may be recovered with the attainment of a new Youkai Watch.

"In exchange for your life, I'll grant you one wish."

Ushiro spends his days looking for people desperate enough to die so he can approach them to convince them to die, so he can eat their souls. Despite how it seems though, he is not completely heartless, offering to grant the people a single wish to come true in exchange for it. However, much to Ushiro's dismay, an upbeat high school girl can actually see him, and on top of that she goes out of her way to convince people not to die.

Being drawn together through some kind of string of fate, the two go on to meet several different people who are struggling with hurtful pasts, perverted presents and foul futures, both doing what they can to help.