Masaki Osoto

Masaki Osoto was the second guest to arrive at Tasokare Hotel after Neko and is the main antagonist of Tasokare Hotel. He was a medical student, serial rapist, and serial killer who arrived at the hotel after slipping on a wet metal board and getting impaled on a pointed fence post.

Appearance
Osoto was a tall young man with neat, dark green hair and yellow-green eyes. In Tasokare Hotel, his attire consisted of plaid wool clothing with a beige-white-green color scheme. He wore a plain white dress shirt paired with a green tie that had a red diagonal stripe near the end. His plaid blazer was draped over his shoulders while black suspenders pulled up his plaid trousers, paired with black two-buckled formal shoes.

In the real world, Osoto wore casual clothing that was vastly different from his style in the hotel. The outfit consisted of a light brown, blue-hooded jacket and a beige cashmere sweater with a light blue button-up shirt underneath. Osoto sported dark grey plaid trousers and the same formal two-buckled shoes he wore in the hotel.

Personality
Osoto was an intelligent, sophisticated, and mild-mannered young man. He was good at solving mysteries and had a very eloquent way of speaking. He had a friendly rivalry against Neko, whom he considers as a foil.

As a serial killer, Osoto avoided detection and suspicion all throughout the span of his criminal history, which proved that he was an excellent and meticulous planner who knew how to get around. However, Osoto was also slightly depressive, which was the driving cause of his psychopathic acts. He felt inferior largely because of the pressure of having successful and well-renowned parents and their borderline-unachievable expectations of him.

Childhood
Despite it seeming like it, Osoto was not born as smart as his parents. Both geniuses, his parents expected him to be better, so they were naturally disappointed in their child. As a kid, Osoto was not praised by them, despite working as hard as he could and studying as much as possible to earn their respect. In his diary, young Osoto mentions that he lost self-esteem in himself and felt as if he was "not good enough" due to this. In an attempt to gain his confidence back, Osoto killed his bird, Pichan. The feeling of being in control of his pet's life gave him confidence and satisfaction. He began harming and killing other animals. Then, he killed a homeless man. Then another person...

Mr. and Mrs. Osoto
Osoto is the only child of two renowned doctors in Kanagawa Prefecture. His parents pressured him to be the perfect student and had unrealistic expectations of him, which made him feel inferior. Osoto felt deep admiration for his parents, and studied hard to meet their expectations. Despite getting good grades, however, Osoto was never praised by his parents, and so he poured out his frustrations through murder.

When he saw the relationship between his parents and Atori, who was impeccable and well-praised, Osoto felt betrayed as they blatantly favored Atori over him. His mother loved Atori so much that she often gave Atori priceless gifts, including a watch that cost millions of yen. His family also sent Atori to represent them in meetings instead of Osoto, using the excuse that he was unable to attend due to "reasons".

Tsukahara Neko
Osoto and Neko have a cat-and-dog relationship. After she exposed Osoto's real identity, Osoto attempted to get rid of her and this sparked a somewhat friendly rivalry between them. He had even once implied that she was the Sherlock Holmes to his Moriarty. However, he does end up helping her a few times in the game and often had humorous banters with her. She only ends up truly fearing and despising him after searching his basement and learning about his secrets. In the True Ending, Neko will prevent him from killing Atori in the real world by fighting and dragging him to hell, which ends their rivalry. In Osoto's special alternate ending, Neko can choose to become his friend as long as he does not lay a hand on Atori. In this ending, it was shown that they truly enjoyed each other's company despite their despicable setup. Overall, in a way, Osoto respected her as the only person who could truly understand him.

Haruto Atori
In Tasokare Hotel, Osoto was initially shown to respect Atori and often thought highly of him in conversations with Neko. Although Atori was wary of Osoto after learning about his criminal background, Osoto valued Atori for being an excellent worker. Osoto was also jealous of Atori in the real world for being favored by his own parents over him. Since Atori managed to gain respect from Osoto's parents, it's very likely that Osoto began admiring him due to this, even though his feelings of jealousy remained. He soon became more and more obsessed with Atori to the point of stalking. After a series of uncanny coincidences, Osoto made the impulsive decision to murder him, which was the reason Atori was sent to Tasokare Hotel. There, Osoto continued his obsession with Atori by attempting to eat him, believing that this way he could "become" Atori. Osoto considered Atori his rival and his destiny.

Kiriko
Osoto and Kiriko got along well due to similar interests and their shared fascination with Neko. They were regular customers of Menow's bar where they often conversed.

Trivia

 * Osoto is the last character to officially be dead in the True Ending after being sent straight to hell by Neko.
 * In one alternate ending, Osoto is alive and Neko agrees to become friends with him, even offering to help him with his crimes, so long as he doesn't lay a hand on Atori.
 * Osoto believes that whatever he ingests will soon become part of his identity and blood, which ultimately drives him to kidnap and attempt to cannibalize Atori in Chapter 6.
 * If Neko leaves the hotel to protect herself from Osoto in Chapter 6, he will also leave the hotel and kill the oblivious Tsukahara in the real world, as he will be one of the rare people who remember their life in the hotel. This alternate ending also reveals that Osoto is alive in the real world like Neko.