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 sometime after the World Domination Arc. It revolves around a trip taken by Mob, Reigen, and friends to the Ibogami Hot Springs around wintertime.

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 recently had a cold and wants him to investigate rumors of a "parallel world" that was getting them bad reviews. After hearing 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 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 repeatedly. Serizawa believes it's the rumored "parallel world".

Cut to Mob and Ritsu sitting in their seats on the train, with Reigen and Serizawa sleeping peacefully. The train arrives at the Ibogami Hot Springs, and Mob pulls the two sleepers off the train. They meet Teruki at the station, and head to the resort early. 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 tells 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, Reigen and Serizawa remain asleep, their minds trapped in the train car in a parallel world. Reigen fails to hide his fear, so Serizawa begins to look around. Unlike Reigen, when Serizawa exits the train car he wakes up just in time for dinner. They worry about Reigen, but Serizawa assures them he's tired of investigating the parallel world.

Meanwhile, Reigen grows hungrier by the minute. Serizawa returns to the train car world and guesses that they got pulled into the parallel world because they were asleep when the train passed through the Ibogami Tunnel. Reigen is still unaware that Serizawa even woke up, and is confused when he leaves the car to take a bath. While Serizawa enjoys the inn, Reigen leaps from the train window, only to somehow land back in the same train car. Losing all hope, Reigen scrawls messages on the walls and seats, muttering to himself.

Serizawa returns with food, much to Reigen's relief. He then realizes that Serizawa was never trapped in the parallel world, and asks him to bring Mob and the others in. With everyone present, Reigen orders them to destroy the parallel world, but they point out that the mountain in the distance contains strong energy. Mob levitates the train off the tracks and toward the mountain, where they find a large orb resembling a sculpture of the god Ibogami from the inn, but surrounded by a goop-like substance. They attack the goop with their psychic powers, only to anger it into attacking the levitating train, where they finally finish it off. Dimple tastes the goop, noting its saltiness. They all wake up simultaneously.

Dimple investigates the source of the goop, flying up Reigen's client's nose to discover a lump in her nostril. He deduces that the family running the Ibogami Hot Springs developed psychic powers that sealed the parallel world without realizing it, and which manifested in a growth 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 have 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 the Spirits and Such Consultation Office with a set of business cards. However, it's revealed that the client's mother just came down with a cold, and Reigen, unfortunately, falls asleep just as they pass back through Ibogami Tunnel.