From Glitchtale Wiki
My Promise is the 5th episode in Season 2 of Glitchtale, and was released on April 6, 2018.
The episode starts with Betty having a fit of rage about the fact that she is the one to retreat and run away, even though she is supposed to be the one feared. Betty then yells at Akumu to show her the souls she has. Akumu then turns into a pink hemisphere per Betty's command and shows the souls they have collected. Seeing most of the souls are partially corrupted by HATE, Betty breaks several of them, saying she won't use HATE to win. However, as she begins to break Asriel's soul, she decides to keep Asriel's soul with HATE, drain the soul of Cam, and order Akumu to destroy the rest.
After this, she tosses a spear at Akumu, which impales and absorbs them, and then impales herself in the chest, thus becoming one with Akumu. She then turns into her true form, which results in her entire eye becoming pink, with her sclera, iris, and pupils becoming a lighter shade of pink than the rest of her eye. She then asks Asriel, who has been reformed using HATE, if they're ready to hunt down those who hurt him the most.
Meanwhile, Jessica confides to Undyne that she feels she has made nothing but mistakes in her life. In response, Undyne confesses that she feels responsible for Alphys' demise, not Betty, since she was the one to pierce Alphys' soul directly.
However, this calming moment quickly comes to an end upon them hearing rather disturbing noises, causing Jessica to investigate and discover that pink blobs managed to break the windows and get into the house.
She manages to kill a blob with the AMR Gun, but her soul begins to crack more. Meanwhile, Undyne fights some others off with her spear. Another pink creature then grabs Jessica after failing to shoot it due to her soul cracking. She screams to Undyne for help, but Undyne can't toss her spear towards the pink creature due to suffering a hallucination of Alphys being in Jessica's place about to be murdered instead. Without Undyne's intervention, the pink creature stabs Jessica in the stomach. This finally snaps Undyne out of her hallucination right before Asgore's trident is thrown at the pink creature, killing it. Jessica then passes out from her injury.
Asgore and the others arrive on the scene, with Sans still in his comatose state. Gaster heads down to his lab in the Underground with Sans and Papyrus. Ronan then calls Jessica's phone and Asgore answers before telling Ronan about Jessica's situation. He asks Ronan to help regroup everyone to a safe location. Ronan decides to regroup at the school, a decision which Toriel objects to. However, Asgore tells Toriel that she resigned her seat as Queen of the Monsters when she fled Asgore and does not have any authority in this situation.
In the lab, Gaster tries to remember his password. Suddenly, the lab triggers him into remembering flashbacks of his time in the Void. Papyrus worries about Gaster and his PTSD, but they press on to the laboratory. Gaster has Papyrus lay Sans down in a special ICU-like bed and then asks Papyrus to get him some supplies. While Papyrus is busy, Gaster views Sans's condition on the screen. It says Sans is fallen down which is essentially a terminal condition where he will turn into dust soon. Gaster is horrified at the results as he stares at the screen in disbelief. When Papyrus gets back, Gaster hastily shuts off the computer so that Papyrus won't see his brother's diagnosis. When Papyrus asks about Sans' condition, Gaster lies to Papyrus that Sans' condition is stable and he'll recover. Papyrus asks to help Gaster with anything multiple times, but Gaster keeps saying no to the point of summoning his Chroma hands in anger before realizing what he just did and calming down.
Frisk, Asgore, Toriel, and Undyne meet in the living room about Betty. They ask Frisk why he didn't tell them about Betty. Frisk apologizes, saying that he thought he could do it on his own and didn't want to bother other people. The group accepts his apology as Asgore explains that Betty is, in fact, a spell "whose only purpose is to cause chaos." Gaster enters the room, interrupting Frisk who was talking about how it's his fault Asriel was captured.
When Asgore attempts to get an update on Sans' condition, Gaster is unwilling to tell Asgore and instead tells him, "not worry about matters that don't concern him." They discuss defeating Betty and how to free Asriel from HATE. After a brief conversation, Asgore creates a plan to defend the school. Gaster says Toriel and Asgore must save Asriel who is corrupted by HATE. Asgore tells Undyne to handle Alphys under the impression that she's able to be saved by Betty the way Asriel can be. However, Asgore doesn't know Undyne was the one who killed Alphys.
The city suffers an explosion, which draws the attention of the crew and they set out. A little girl is injured by one of the pink creatures, but it's destroyed by Ronan, who then tells the girl to get to the school.
Betty sits on a building, seeing Frisk, Toriel, and Asgore coming. As a result, Betty comes down, and says she was excited to fight all of them, but mostly only wanted to fight Frisk and finish what they started. As for Toriel and Asgore, Betty forces them to fight their son, Asriel, whose HATE is enhanced by his parents' turbulent history. As Asriel begins fighting the duo, they try to calm him down and stop fighting but fail to do so. Frisk and Betty start fighting again and Betty notices Frisk looks terrified. Betty asks if Frisk is scared because of her new appearance or because he knows he can’t win this battle. Eventually, Asgore gets stabbed in his upper chest by Asriel. While Frisk and Toriel don't get hurt, they can't manage to win and clearly cannot free Asriel from HATE, so they all decide to retreat.
Having read about the "Fallen Down" stage Sans is in, Gaster attempts to look for a cure. The three fighters show up, and when Gaster sees Toriel healing Asgore's wound, Gaster becomes concerned. However, Asgore dismisses it, saying, "Don't worry. I'll be fine." Both Toriel and Asgore worry if they will lose Asriel again.
Frisk and Gaster talk about Gaster's failed experiment. Frisk says the experiment failed due to a lack of Determination and that if he recreates what Gaster did but using his own soul, he would succeed. Gaster is surprised at first but understands why Frisk would want to do it, which is to "fix his (Frisk's) condition," and proceeds with it. This experiment sends Frisk into the Void, where he meets Chara. Chara, angry at Frisk for using his HATE on him, punches him in the face. Chara berates Frisk for abandoning and blaming him for all of his mistakes. Frisk agrees that he shouldn't ask Chara for help, but people they both care about are in danger and Frisk cannot solve this alone. Chara then asks why Frisk doesn't just reset. Frisk explains to Chara that he destroyed the RESET button and cannot save or load anymore. He then offers a solution, proposing to replace Chara in this timeline and offer Chara his soul. He tells Chara this will only mean that they'll switch the places they were in back in the Underground (i.e., Frisk following Chara around instead of Chara following Frisk around). Chara chides Frisk for this being the only solution he can come up with and for him being able to only last a month without a catastrophe occurring. Despite this, Chara agrees to the solution. Frisk then passes the Determination soul to Chara, pushing the experiment to the point of no return. Frisk confesses that he lied to Chara about the "ghost following"' in the Underground, and what will really happen is that he will be erased from existence (Frisk is glitched, so if he remains in the timeline, the timeline will become more unstable and erase itself eventually). Chara will lead a normal life devoid of any memory of Frisk. Chara frantically protests, but Frisk replaces himself anyway. This changes everyone's memories, while still keeping the events that actually happened the same, and sends Chara to the Surface in Frisk's place. This ultimately results in Frisk being erased from existence. Frisk's final words to Chara are: "Keep my promise".
- Despite the apparent replacement performed by Frisk, which had removed him from reality and inserted Chara, the timeline of events, which is to say, everything that quite literally happened, had not been altered. Instead, it was the memories of each individual that had interacted with Frisk up until his disappearance that had been altered. Where Frisk had been, Chara is instead remembered to have been, and to varying degrees, Frisk's actions are credited to Chara. This appears to not include certain events that would present Chara negatively to other people, such as the argument had between Frisk and Asriel.
- The text after the after-credits scene was the exact words goner kid would say in the Undertale game.