Youkai Watch Movie 4: Shadow Side - Oni-ou no Fukkatsu
English title: Yo-kai Watch Shadowside: The Return of the Oni King
Japanese title: 映画　妖怪ウォッチ　シャドウサイド　鬼王の復活
Alternative titles: Eiga Youkai Watch: Shadow Side - Oni Ou no Fukkatsu
Type: Movie
Source: Game
Episodes: 1
Status: Finished Airing
Aired: Dec 16, 2017
Duration: 1 hr 34 min
Rating: G - All Ages
Studios: OLM
Genres: Supernatural
Themes: Mythology
Demographics: Kids

Taking place 30 years after the events of the original Youkai Watch TV series. There was once a 11 year old boy named Keita Amano who held a wristwatch that could command Youkai, he would make friends with the Youkai and fulfill a great many deeds. But when the boy grew up, he lost his ability to see Youkai. And as for the wristwatch that could control Youkai, its existence threatened to disturb the balance between human and Youkai worlds, so it was cast away into oblivion beyond time and space. Soon ... the story of the Youkai controlling wristwatch became but a legend. But then, something took place after many, many years had passed ... an epidemic Youkai virus known as Onimaro started affecting people with malevolent intentions and is spreading indefinitely, turning them into Kaodeka Oni and causing chaos throughout the city. With the end near, only the ones chosen by a new Youkai Watch can stand up against the upcoming threat and would save both Youkai and humans from certain destruction.

(Source: Yo-kai Watch Wiki)