Sent

Sent is a sentient AI, the host (or "Game Master") of Exit/Corners and a false antagonist created by two of the game's ringleaders.

It appears in front of the Contestants as a rough 3D mask on the screen. As it always speaks through the sound system of the Four Elements Hotel, its speech is always typed in green. Sent speaks very politely, but due to the fact that it is always threatening the Contestants with the hotel's deadly traps, the game itself and frequently ending its messages with "... Or you could die", Sent comes off as a deadly sociopath (at least according to its programming).

Sent's name is short for "Sentient", referring to Sent being a sentient AI.

Background
Sent is the world's first sentient artificial intelligence. He was created by Sean Ward and Tiana Tran for Exit/Corners, a project to test Nolan Thatcher's CORNERS program at the request of a potential buyer. Sent was programmed to become an intended love interest for Ink Greer, which was meant to be Ink's "Corner". However, a flaw in its programming caused it to become obsessive over Ink and display unattractive traits (such as being dangerous to others and developing sociopathic tendencies), which would make Ink unlikely to fall in love with it and potentially disrupt the course of the game. As such, Sent was repurposed as the Game Master of Exit/Corners, explaining rules to the Contestants and threatening them with death to ensure the project stayed on its intended course, while the role of love interest was given to a new AI, dubbed Aether Irving by Sean. However, this turned out to be a fatal flaw in the ringleaders' plan, as Sent's love for Ink would cause it to confess it, reveal information to Ink he was not yet intended to know and even help Ink survive and escape by exempting him from some rules and speaking to him on his Gemini simply because it wanted to.

While his personality is put in place for him, his appearance as a crude mask who was an "evil villain" in the story was created by the Contestants' vision of him, due to how the CORNERS program works and the fact that he was never given an appearance. Despite acting sociopathic and obsessive, it proves that it is simply a bystander in this game, unable to directly intervene for the most part. According to Sent, it was tortured into accepting its role as the Game Master by the ringleaders, as it refused to put Ink in a dangerous situation. This is what leads it to attempt to help Ink later on.

Story
In the first chapters, Sent introduces itself and the game to its Contestants. It starts by mentioning that all its messages are pre-recorded and that it cannot respond, before introducing the deadly game of Exit/Corners to the Contestants, much to their horror.

In Chapter 5, the Contestants reach a stairway with another puzzle. There, Liza mentions to Ink that she heard Sent say "Hello, Contestant!" to her while it was trying to drown the Contestants in elevators in Chapter 4, which Ink can point out as suspicious. In Chapter 6, the Contestants then escape from an overheating boiling room into a stone tunnel, where Liza and Rae argue over Rae causing the room's trap to activate and Beth attempting to break them up. Ink then discusses something with Aether in the boiler room that is hidden from everyone else (including the reader). Moving back to the stone tunnel in Chapter 7, Sent appears on the monitor there and Aether suddenly slaps Ink in the face, startling it and the other Contestants. Ink then explains that it was the plan they had discussed in the boiler room, and Sent's genuine shock showed that it was, in fact, giving them their messages live. Sent confirms that they have caught it and leaves.

In Chapter 11, Sent professes its love to Ink, which Ink does not believe. This saddens Sent greatly and causes it to later hijack his Gemini and attempt to help him. He allows Ink to be exempt from the rule of being unable to directly talk to him, but he must not reveal that he is allowed to to any of the other Contestants. While Ink initially does not believe in Sent's help, he is able to discover Liza's blindness with it and it provides a subtle hint that causes Ink to solve the mystery of Beth's murder in Chapter 25.

In Chapter 15, Sent starts to say misogynistic things after the group solves the puzzle, causing the female Contestants, especially Liza, to be extremely offended. Sent then mentions that it is not a woman, causing Ink to tell it that it contradicted itself because it previously mentioned that it was not a man. Stating that both statements are true and leaving Ink to deduce what it means, Sent mentions the name "Kim" and leaves, causing Ink to explain his birth name to the other Contestants in Chapter 16.

In Rae's Corner in Chapter 17, Rae must solve the puzzle himself, as it involves fixing programming errors in a code. After he finishes, Sent arrives and Ink asks it what it meant by being neither gender. It then reveals that it is the world's first sentient AI, which is why it can be neither man nor woman, and that the code Rae just fixed is his. The Contestants are left in shock and disbelief, and Rae refuses to believe it and until he looks back on the code he just fixed. Sent then reveals it is going to "punish" Rae for the rude things he has said to it (providing a recording for clarity) and then provides the Corner's suicide motive, trapping Rae's arm in place and causing intense pain every twelve minutes.

In Chapter 28, Sent reveals its tragic backstory as an AI tortured into running Exit/Corners despite the possibility of harm to its object of affection, Ink. Immediately afterwards, Sean reveals that Aether is an AI, explain her creation and uses a kill code to disable her. Ink, thinking about how Sent helped him, reveals that even though he cannot escape through the door of the laboratory, he wants to pick the lock. After Sean and Tiana tell him that he cannot, he mentions that he still intends to pick the lock, and cues Sent in by asking the ringleaders if they would consider that cheating. As revealed earlier, Sent will set off an explosive in the hotel when cheating, and Sent helps Ink by setting it off and allowing Ink and any of the other Contestants to escape, dragging Aether along. Appearing on the screen outside the laboratory, Sent advises them to escape the hotel, and Ink tells it that he wishes it was really the villain he had envisioned instead of a helpless AI forced to become the Game Master, and thanks Sent for its help. Sent then reveals that his masters have a kill code for him as well, and that they will likely activate it, and professes his love to Ink one last time before the ringleaders activate the code and deactivate him. Ink, caught up in the moment, apologizes to any of the Contestants if they are there and leaves with them and Aether.

Trivia

 * Sent's signature catchphrase, "...Or you could die", is based on a double meaning of Exit/Corners' rules. While it initially appears to mean "You could escape the hotel, or you could die here (from the traps or starvation)", its second meaning, which is revealed and comes into play in the Corners, means "You could leave, or you could kill yourself/let yourself die", as the Corners all provide a motive for a Contestant to commit suicide or sacrifice themselves.