Satō Matsuzaka

Satō Matsuzaka is the main protagonist of the 2015 psychological horror anime Happy Sugar Life and its 2018 anime adaptation.

Description
Satō is a high schooler known for being "easy", once admitting to have been with millions of boys, only changing partners every three days. This all changed when she discovered Shio Kobe, a young girl who was seemingly left by herself. Becoming enamored by her, Satō kidnaps her, believing that it was under the impression that she had fallen in love with the young girl. Sometime later, Satō and Shio arrive to an apartment, and Satō proceeds to murder the manager of the hospital. After murdering him, she hacks up the body, placing the body parts in three different bags which she tried to dispose of sometime later.

Gradually, Satō decided to work harder in order to support her and Shio. After one job she had for a short time, Satō learns about a restaurant known as the Princess Imperal, and decides to work there. While there, Mitsuboshi, a young man who works as a waiter for the restaurant, asks Satō out for a date only to be turned down. From there, it appeared as though Mitsuboshi quit the restaurant out of despair of having been rejected. When the employees get their checks, Satō notices that her check was short despite working more hours for the restaurant. While conversing with her, Satō notices her cabinet, realizing that Mitsuboshi was actually trapped in the cabinet. The manager explains to her that she had kidnapped Mitsuboshi because she overheard him say that he loved Satō instead of her. Enraged by this, she kidnapped Mitsuboshi, forcefully molesting him as her way of making him love her. Unfortunately for her, Satō filmed her confession on her phone, and suggests that she leak the footage to the public lest she be given her due. She opens the door to the cabinet and looks at the bound Mitsuboshi with pity before leaving.

Later on in the manga, Satō's friend, Shouko Hida finds Shio and takes a picture of her with her phone. Despite offering to hand over the phone to her, Sato slits her throat out of fear that she might go to the authorities about what she had discovered. As Shouko was the only link that Sato had with the outside world, Sato became more unhinged.

Trivia

 * Her exact obsession with Shio is uncertain. She definitely loves her, but it is not in a sexual manner.