Undertale is a role-playing game where you don’t have to kill anyone! Undertale was created by Toby Fox and was released on September 15, 2015.
Long ago, two races ruled over the Earth as equals: humans and monsters. One day, a war broke out between them and, after a long series of battles, the humans were victorious. Seven of their greatest magicians sealed the monsters to the Underground with a magic barrier, while the humans took control of the surface. However, the barrier is not a perfect seal, and the only point of entrance to the Underground is Mount Ebott.
Many years after the war, a human child falls through Mount Ebott and into the Ruins—a small section of the Underground. Though the protagonist is unnamed throughout most of the game, later dialogue reveals their name as Frisk. They soon encounter Flowey, a sentient flower who attempts to kill Frisk for his own amusement. Flowey is stopped by a motherly monster named Toriel, who teaches the child how to solve puzzles and survive conflict in the Underground. However, she also reveals her intentions to adopt Frisk and force them to live with her in the Ruins forever. After a boss fight with Toriel, she allows Frisk to exit the Ruins.
Frisk ventures through the Underground in order to reach the barrier located in the castle of Asgore Dreemurr, the king of the monsters. They learn that, to destroy the barrier and free the monsters, the king needs seven human souls—of which he has six. Throughout the game, they meet many monsters, which they may kill or try to resolve the encounter peacefully. Among the monsters that the player encounters are Sans, a wisecracking and slothful skeleton; Papyrus, Sans’ enthusiastic yet incompetent brother; Undyne, the boisterous head of the royal guard; Alphys, the kingdom’s reclusive royal scientist; and Mettaton, a robot with dreams of super-stardom. The choices that the player makes determine the route that they take through the story, as well as the ending sequence. Further playthroughs are irreversibly affected by all routes, with differences in dialogue dependent on the decisions made in previous playthroughs.
If Frisk at any point kills a monster in combat, or if relationships with certain characters are not fully developed, the plot proceeds linearly with Frisk progressing to Asgore’s castle. Upon arrival, Alphys reveals that it is only possible to leave the barrier with a monster soul, meaning that they must kill Asgore. Before Frisk meets Asgore, Sans stops them at the “Final Corridor”, and reveals that “LV”, or “LOVE” is actually an acronym standing for “Level Of ViolencE”. “EXP”, as well, is an acronym, standing for “EXecution Points”. Sans then judges Frisk, based on how much LV they’ve accrued, and what bosses they have or haven’t killed. Regardless, he lets them pass. Frisk then confronts Asgore and begins to follow through with taking Asgore’s SOUL, though the player may eventually choose to spare him, rather than dealing the final blow. Unfortunately, Flowey appears and kills Asgore regardless, stealing the human souls and transforming into a monstrous abomination that the player must then defeat. If the player, at any time, dies in-battle, the game closes. Flowey also steals the ability to save and reset the game from the player, revealing the mechanic as a feature of the game’s universe rather than simply a tool for the player to use. After the player beats Flowey with the help of the rebelling human souls, Frisk wakes up and receives a final phone call from Sans informing them of the state of the Underground after their departure.
However, if the player successfully resolves every encounter in the game peacefully and befriends key characters, Frisk learns that Flowey is the deceased son of Asgore and Toriel—Asriel, inadvertently revived as a result of Alphys attempting to give the will to live to a vessel with no soul. Despite Toriel intervening before Frisk fights Asgore, Flowey ambushes the cast at the barrier and absorbs the souls of all the monsters in the underground. Taking the form of Asriel once more, the souls give him the power of an angel of death—however, he acquires with them the love the monsters feel towards Frisk and ultimately loses the will to fight, instead using his power to destroy the barrier and free the monsters for good before reverting back to Flowey. The game concludes as the monsters begin to integrate once more with the surface world. If the player begins a new playthrough after achieving this ending, Flowey berates the player for overriding the characters’ happy ending for their own continued amusement.
A significant change comes as a result of killing every monster in the Underground in one playthrough; Frisk becomes influenced by a malevolent entity known by the name chosen at the start of the game (canonically “Chara”), another human who previously fell into the Underground and was adopted by the Dreemurrs. Chara journeyed to the mountain because they hated humanity; they died soon after, with Asriel also being slain the same night when he attempted to return their body to the human world. As Frisk reaches Asgore’s castle, Sans attempts to stop them in a climactic battle, but Frisk is ultimately successful in slaying Sans, Asgore and finally Flowey, despite the latter’s attempts to win Frisk’s goodwill as a former friend of Chara. Out of control of the player, Chara destroys the world and mocks the player should they attempt to reverse their decision through resetting the game. If the player agrees with the demand for their soul in exchange for resetting the world, Chara makes several appearances in later playthroughs and this change is irreversible without the deletion or manual editing of hidden game files.