|Name in Japanese||因果律のメルト|
|Romaji Translation||Ingaritsu no Meruto|
|Release Date||August 24, 2011|
|Episode Director||Kanji Wakabayashi|
|Previous||Episode 20: Finalize Apoptosis|
|Next||Episode 22: Being Meltdown|
Despite his best efforts, Okabe is forced to watch as Mayuri dies yet another agonizing death. Subsequently, the mad scientist finds himself faced with a horrific decision: choosing which of his lab members will die!
Daru begins to make the final preparations, but Okabe quickly tells him it's not necessary to do so. He then quickly runs onto the roof, laying flat on his back. Daru then leaves while Mayuri arrives, asking Kurisu to come with her to the convention again. Mayuri eventually finds Okabe on the roof and gives him some water and her hat to shield him from the sun. She then prepares to leave for the convention, but Okabe stops her and decides to come along. As they get there, Okabe concludes that, based on the D-mails getting repeatedly pushed back, Mayuri will die that very day.
Mayuri quickly comes up to him and offers him some books she bought about a new mecha show, but Okabe rides it off, saying he is preoccupied with fighting The Organization and has to leave to set up ninjas, asking her to meet him there in a few hours. At the same time, Kurisu is asked by Daru to get one of his playboy books in Okabe's belongings, deciding that she will sue later. Okabe then calls her and asks if they have made any "progress". This prompts Kurisu to ask what is going on. Okabe tells her he plans to save Mayuri with the already-erased D-mails without going to another world line, but refuses to say why, only saying there are unforeseen developments. Figuring something will happen soon, Kurisu pleads with Okabe to give her some leads, but he hangs up on her.
Evening comes, and Mayuri asks about food, but Okabe, after some moments, comes to the realization it's almost about when Mayuri is supposed to die. They head into an alleyway, where Mayuri asks why he came along when he barely looked at anything while he was there, noting that this was the first time he ever came. This seems to cheer Okabe up, and they talk about getting the whole lab together next time to do a group cosplay. Just then, a car appears in front of them, and the clocks stop again. Realizing Mayuri will die again, Okabe rushes away with her away from the car and places her in an alley. He then charges the car, hoping that by him dying they will not harm her. Instead, Mayuri comes up and pushes him out of the way, consequently getting hit by the car and dying in Okabe's arms. Overwhelmed, Okabe goes back to the lab and rests Mayuri's body on the couch. He sees a note from Kurisu saying that they need to talk, but ignoring it Okabe uses the phone wave again.
August 13th, 2010: 3:53 PM
Okabe transports himself back to when Daru is commencing the hacking. This time, Kurisu and Daru see Okabe's downtrodden face and proceed to not go through with it.
August 15th, 2010: 1:53 PM
Okabe lies flat on his back again, staring up at the sky. This time Kurisu comes up, admitting that she's worried about Okabe after he said he wanted to be left alone. Okabe, still avoiding the subject, says he's only being a law-abiding citizen. Kurisu mocks this since evil geniuses don't typically accept such things, but this causes Okabe to snap, saying that he's no evil genius and that Hououin Kyoma is a piece of child's play. Surprised, Kurisu realizes that he time leapt again, and asks what happened, arguing that they are a good team. But Okabe says that, even after making Faris, Ruka, and Moeka undo their D-mails, they still haven't made any progress, and deciding he's had enough, Okabe proceeds to take his phone and prepare to throw it off the building. Kurisu manages to catch his arm before he can, nearly hugging him in the process, and tells him to tell her so that she can help, since he cried about it. Okabe then finally tells Kurisu about the D-mail, and after he finishes Mayuri calls him. She asks him if he is doing okay after Daru mentioned Okabe's crying to her. He says he's okay, and after a brief talk about ninjas. After Mayuri hangs up, Kurisu tells Okabe to go find her, since moping over herself pisses her off.
Okabe takes her advice, and learns from Daru that she headed out per the guidance of one of her cosplayer friends. Mayuri is revealed to have gone to her grandmother's grave, where it is revealed that Mayuri has been experiencing her deaths from the other world lines via her dreams, and asks what they mean. She also mentions that in each of the "dreams", Okabe tries to rescue her but he can't seem to hear her when she says "thank you" and is always holding back tears; at the same time, Okabe is revealed to have found her but is standing elsewhere listening solemnly to her. Deciding to change the subject to something else, Mayuri recalls how she first came to the lab. It was snowing back then, and Okabe wasn't even home, so Mayuri decided to clean the place up. She then welcomed Okabe back home, and from then on would spend a couple of hours in near silence with Okabe. Even then, there was more talking than they do right then. Mayuri figures that Okabe is hurting inside, and that it's all her fault, as well as that she doesn't want it to go down this way. Okabe then reveals himself, saying he won't let her out of his sight since she is his hostage. He then says that he will tell her eventually what the issue is, and leaves with her to get another Oopa.
That night, Kurisu comes to Radio Kaikan building where Suzuha's time machine had crashed, and within the darkness she found the room where she was stabbed in another worldline.