Mob Psycho 100 II: The First Spirits and Such Company Trip

Mob Psycho 100 II: The First Spirits and Such Company Trip ~A Journey that Mends the Heart and Heals the Soul~ is an OVA produced by Studio BONES and released on September 24, 2019. It is an original story not found in the manga, taking place some time after the World Domination Arc. It revolves around a trip taken by Mob, Reigen, and friends to the Ibogami Hot Springs around winter time.

Plot
Reigen meets up with Mob and Ritsu at the train station, followed by Serizawa, to head to the Ibogami Hot Springs for some vacation time. In a flashback, it's revealed that Reigen was actually approached by one of the owners of the resort. She has had a cold recently, and wants him to investigate rumors of a "parallel world" that was getting them bad reviews for her. After learning that she would pay for all travel expenses, Reigen couldn't pass up such an opportunity.

The group boards the train and heads to the Zebra Prefecture where the hot springs are located, and they find that Dimple has tagged along. Mob and Ritsu head to the bathroom, while Reigen and Serizawa both fall asleep. The train passes through the Ibogami Tunnel, transporting the train to a dark wasteland with a single mountain looming in the distance. Reigen assumes Mob has something to do with it and goes to look for him, but finds himself stuck in a loop of entering and exiting the same train car over and over again. Serizawa believes it's the "parallel world" the rumors were about.

Cut to Mob and Ritsu sitting back in their seats on the train, with Reigen and Serizawa sleeping peacefully. The train arrives at the Ibogami Hot Springs, and Mob gets their two sleeping companions off the train with his telekinesis. At the station they find Teruki, who headed to the resort early to scout it out. The group meets Reigen's client, who brings them to an inn where they will stay for the night. As they explore the inn, Teruki explains the legend of a god named Ibogami who allegedly sealed a gateway to a dark world years ago.

While Mob, Ritsu, Dimple, and Teruki enjoy the hot springs at the resort, Reigen and Serizawa continue to sleep, their minds trapped in the train car in the parallel world. Reigen is struggling to hide his fear, so Serizawa begins to look around. When he exits the train car, he wakes up, unlike Reigen, just in time for dinner with the others. They express concern for Reigen, but Serizawa assures them he's tired from working hard, investigating the parallel world.

Meanwhile, Reigen is growing hungrier by the minute. Serizawa returns to the train car and explains to Reigen that it's likely because they were asleep when the train went through the Ibogami Tunnel that they were put in the parallel world. Reigen still isn't aware that Serizawa even woke up, and is confused when he decides he's going to take a bath and leaves the train car again. While Serizawa socializes with the others, Reigen considers leaping from the train window - however, when he does he lands right back in the same train car. He loses all hope, and begins to scrawl messages on the walls and seats muttering to himself.

Serizawa returns again, much to Reigen's relief. He brings food, which Reigen quickly gulps down. He then realizes that Serizawa was able to escape the parallel world without him even noticing, and asks him to bring Mob and the others in with him. He asks the group to destroy the parallel world, and they point out that the mountain in the distance is the source of a strong energy. Mob lifts the train off the tracks and levitates it towards the mountain, where they find a large orb resembling a sculpture of the god Ibogami from the inn surrounded by a goop-like substance. The espers attack the goop with their collective psychic powers, only to anger it into attacking the levitating train where they finally finish it off. Dimple takes a taste of the goop, noting its odd saltiness. They all then wake up simultaneously.

Dimple investigates the source of the goop, flying up Reigen's client's nose where he discovers a wart inside her nostrils. He deduces that the family that runs the Ibogami Hot Springs developed psychic powers that sealed the parallel world without realizing it, and that it manifested in a lump in their noses. Because she had a cold, her psychic powers were weakened, reopening the other world.

The next morning, Reigen tells the client that they resolved the situation and gives her cold medicine to take if the parallel world opens again. On the train back home, he officially welcomes Serizawa to Spirits and Such Consultation Services by giving him a set of business cards. However, it's revealed that the client's mother also just came down with a cold, and Reigen unfortunately falls asleep just before going back through Ibogami Tunnel.