Yandere Simulator is a stealth action video game for PC currently under development by American game developer Alex Mahan, also known under the "YandereDev" alias. The game centers upon an obsessively lovesick schoolgirl named Ayano Aishi, nicknamed "Yandere-chan", who has taken it upon herself to eliminate anyone she believes is attracting her "senpai's" attention. Development of the game began in 2014 and it had achieved a considerable amount of attention online on platforms such as YouTube in 2015, leading to millions of downloads of pre-release versions of the game. However, Yandere Simulator has been stuck in development hell, and there have been accusations against Mahan of stolen content amongst other controversies.

The player controls Ayano Aishi (nicknamed Yandere-chan), an apathetic Japanese high school girl who has developed a crush on Taro Yamada, a fellow student only ever referred to in game as "Senpai". Over the course of ten weeks, a different girl will fall in love with Taro, becoming a target for Ayano to eliminate. The player has the ability to kidnap, torture, poison, electrocute, matchmake, befriend, betray, and drown rivals, befriend other schoolgirls, play small mini games, access a street where the player can earn money by playing a maid café minigame, spend money at shops to buy different types of items, and more.

1980s Mode centers upon Ryoba, a teenage girl who has become obsessed with a popular male student named Jokichi and the future mother of Ayano. Ten rivals stand in her way and a journalist is watching her every move, aware of her homicidal tendencies. In order to prevent detection, Ryoba must plan her moves out carefully. If she acts suspiciously or does not clean up after her murders properly she will gain a "guilty" point. She can counteract these by befriending fellow students and maintaining a good reputation. Ryoba is eventually brought to trial after eliminating her rivals; if she has collected more guilty points than innocent ones she will be found guilty and imprisoned. If found innocent she will kidnap Jokichi and keep him in her basement until he agrees to enter into a relationship with her.

Yandere Simulator is developed by YandereDev, a freelance game developer identified as Alex Mahan and based in Temecula, California. He first pitched the idea on 4chan around 2014, and after receiving positive feedback, decided to begin development. Mahan has stated that the series Mirai Nikki and School Days were inspirations for the game. In order to work on the game full-time, Mahan opened a Patreon account in 2016; he has stated that prior to this he worked as a freelance programmer.

On March 1, 2017, YandereDev announced a partnership with tinyBuild that would help him polish, promote, and publish the game. On June 10, 2018, YandereDev announced that the partnership with the company had ended in December 2017 due to tinyBuild's programmer and Mahan's code conflicting.

On August 31, 2020, the game's first demo was released along with Ayano's first rival, Osana Najimi.

A prequel mode named "1980s Mode" was released on October 10, 2021. This mode is a story mode that follows Ayano Aishi's mother, Ryoba Aishi, and follows the same storyline as the main story. The developer has stated that this mode was created to test the game's various systems. 1980s Mode features VHS effects and a new soundtrack in order to differentiate it from the main story.

The game has received criticism over its content and themes, with the most common criticism centering upon the presence of sexuality and murder. In their 2022 doctoral dissertation, Kristian A. Bjørkelo noted that some hearing about or playing the game found it transgressive due to the themes of sexuality and murder, while others took more exception to an update that would allow players to kill cats as a way of avoiding police detection. They further noted that Yandere Simulator was an example of a game that conflicted with "the idea that play is harmless fun, something that can be considered for children, a notion that can be referred to as the idealization of play... or the fallacy of play".

Cecilia D'Anastasio, writing for Kotaku, covered the debug version in a 2017 article; she commented that the game had received criticism for "glamorizing suicide, bullying and Bipolar Disorder—allegations that I strongly agree with, despite the game's merits as simulator for sociopathy." D'Anastasio went on to interview Mahan in the same article, who stated that the game "pivots on the archetype of an obsessed, violent stalker, rather than female stereotypes."

In 2016, Yandere Simulator was added to the list of banned games by Twitch for violating the streaming service's policies on extreme content. Mahan was a vocal critic of the ban, claiming that Twitch never explained what prompted its addition to the list and that he would have been willing to "modify minor, innocuous things that were never meant to be the focus of the game, but I would not be willing to remove gameplay mechanics, remove core features, or change the focus of the game." He further criticized the ban as a result of "self-righteous ideologies".

Fans have voiced concerns over how long development of the game has taken. Mahan initially responded to these concerns with an announcement in March 2017 that he would be partnering with TinyBuild; this partnership ended in December of the same year.

In September 2023, allegations were brought against Mahan by a 16-year-old girl claiming that he had been grooming her and released several recordings and transcripts of his actions. After the evidence surfaced several of the game's developers and voice actors, including Ayano's voice actress Michaela Laws, left the project. Mahan later confirmed that "inappropriate" conversations had occurred, but denied that he had deliberately attempted to groom the minor. Following this, the game's development has been on a partial hiatus. In October 2023, Mahan was banned from Twitch in response to the allegations.

• Official website