When a meteor is about to approach Earth, Summer Adams, Cole and Bruno meet up and work together to stop the Onimaro invasion with the power of a new Yo-kai Watch and Yo-kai that can change between Lightside and Shadowside forms.
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.—Wiki
There used to be a boy who could control Yo-kai with a mysterious watch. However, he became unable to see Yo-kai 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 Yo-kai virus Onimaro infects people's malevolent intentions and spreads infinitely. The one chosen by the Yo-kai Watch is the one who can save humanity from its crisis. The bond between humans and Yo-kai may be recovered with the attainment of a new Yo-kai Watch.—Yo-kai Watch Wiki
At the beginning, an imagining voice explains that there was once a boy that could see Yo-kai, and fulfill their deeds. As that boy grew up into an adult, he lost the ability to see Yo-kai, thus causing his Yo-kai Watch to be cast away into oblivion due to its existence threatening to disturb the balance between human and Yo-kai worlds. Over time, the story about a boy that could see Yo-kai became nothing but a legend, but something started to take place thirty years into the future.
A boy named Cole wakes up and looks at the text message at his phone, where he feels depressed because his parents aren't able to come home due to their busy working lives. While Cole gets up, he turns on the television, which is of a news report related to an approaching meteorite. As the news further explains the information about the incoming disaster, Cole walks out of his house, without suspecting some Onimaro following him.
Meanwhile, a girl named Summer Adams is worried about being late for school and tries to get there as fast as she could. When she approaches the bridge, she notices a group of people and a child drowning in the riverbank. Despite the man warning him (then being inspirited by the Onimaro), Summer decides to save the child from drowning and manages to bring them back to dry land.
As she makes her way to school, she gets a flashback about being drowned, but then being saved by a mysterious force. At first, she wondered that it was a hallucination, but it was what inspired her to save other people from drowning. Suddenly, one of her friends Saki notices that Summer is covered in water, who responds by saying she is late for school and would prefer to walk than to take the bus. Summer notices Cole, but walks away from him.
While another boy named Bruno is on his way to school, he notices the huge meteor approaching and rushes back to his home warn his grandmother about it. When his grandmother notices it, she realizes that the threat is worse than imagined and says that it is the result of an Onimaro invasion. Bruno asks what they are, but doesn't know about it and his grandmother says that the invasion will cause doom to be brought upon the world.
When Cole arrives at school he decides not to attend it, while as Summer changes her clothes at the gym lockers she suddenly realizes something about Cole. Back at Bruno's residence, his grandmother further explains about the Onimaro virus, which requires a Yo-kai Watch to stop them. She explains that the Yo-kai Watch was destroyed by the rulers of the Yo-kai World, and it's now nearly impossible to obtain one. Bruno thinks that this information wouldn't be useful, but his grandmother goes on to explain that a different kind of Yo-kai Watch exists, which was created in ancient times. His grandmother gives him a Yo-kai Radar, and rushes out of the house in hope of finding the Yo-kai Watch.
At the Enma Palace in the Yo-kai World, Lord Ananta, the new ruler of the Enma Clan, is annoyed at the lack of visitors and appreciation for him. It also reveals that the previous ruler, Lord Enma is locked inside a cell. A spirit, who is actually Zazel, explains to him about the Onimaro invasion, and Enma replies that they came too early and is worried about the fate of the Yo-kai World. After claiming that all of the Yo-kai Watches were destroyed, Enma explains the existence of the Yo-kai Watch Arcane, which was created by the Genyou tribe a long time ago, and is said to contain bigger power than the other Yo-kai Watches. After asking where it could be located, Enma says that they have it, but the owner of it hasn't been found.
Back in the human world, Cole walks to a video game arcade, while some of the Onimaro follow him. A group of delinquents bump into him by accident and Cole apologizes for it. They suddenly take note of Cole's quiet personality and makes fun of him. After Cole asked them that he was going to get mugged, he is escorted to an alleyway, gets beaten up by them and has his money stolen.
Cole starts to get angry and threatens the delinquents silently, making the Onimaro proud of him and inspirited by them. He suddenly gains power, grabbing one of the delinquents and throwing them onto the garbage bags. The rest try to fight him, but they get thrown around from Cole's newfound strength. When one of the delinquents try to attack him with a pipe, Cole suddenly grows a muscular arm and throws him again, causing them to flee. When the Onimaro inside him question if he liked that strength, they suddenly come out and show themselves in front of Cole.
The Onimaro themselves offer a deal where they give him a share of their power, assuming that Cole liked what he felt then. The Onimaro are proud of Cole's strength, while one of them says that he should make everyone around him exist, whereas Cole realizes that his existence to others has been oblivious throughout his whole life. Cole reluctantly accepts the deal, where the Onimaro suddenly summon the Onimaro Leader and their power is forced into his body, despite feeling startled and scared. Despite having to endure the strength from other Onimaro around him, Cole suddenly takes full advantage of his newfound power and faces himself with a muscular delinquent whom is also inspirited by the Onimaro.
In the meantime, Bruno and his grandmother search for the Yo-kai Watch with the radar in a suburban neighborhood. Bruno asks what the Onimaro are like, where his grandmother exaggerates that they're dangerous and then formally explains that they are like a virus, multiplying when they infect innocent human beings and impossible to prevent once they spread. Bruno asks where Onimaro originated from, while his grandmother further explained that they come from the sky after thousands of years, and they are of extraterrestrial Yo-kai. She also says that they eat up the human's heart, where their animosity builds up until their death and does crime-inducing acts.
While Cole fights the inspirited delinquent, he suddenly gains the upper hand by punching him in the stomach with his muscular arm and finishes him off. The Onimaro praise Cole for his strength where the Onimaro Leader gives him a piece of equipment called the Kigan Gear, which gives him the ability to control other beings under his will. Cole tests the Kigan Gear on the delinquent he took out, and they suddenly obey him while the Onimaro Leader is happy that Cole is worthy of being their new leader.
The Onimaro Leader further assumes Cole that he doesn't like this world, how he doesn't have enough friends, and how he feels unseen towards everyone else. Cole asks the Onimaro Leader if it was the reason why the Onimaro chose him, and they respond that they did, because they noticed the darkness inside of his heart. The Onimaro Leader convinces Cole to build an army of his own with the Kigan Gear, so they can make the whole world aware of his existence. Cole starts to take advantage of this new power, turning the other innocent human beings into Onimaro.
Back at the Yo-kai World, Zazel manages to find a key to unlock the cell where Enma was imprisoned, who had already broken out of it. Enma orders Zazel to quickly stop the Onimaro invasion happening in the human world. When his mentor breaks the news of Enma escaping from the prison cell, Lord Ananta is annoyed at the unexpected situation, while his mentor is surprised that Enma manged to break out of there.
