Rintarou Okabe goes out with his friend Mayuri Shiina to a conference on time travel being held at the radio building in the city. Professor Nakabichi is set to give a speech on time travel, when Okabe hears a rumbling sound. Going to investigate, he runs into a girl genius named Kurisu Makise, who has her own theories.
Kurisu found dead....
Okabe reconnects with Mayuri as she's buying a toy from a machine when the two of them hear a loud scream. Okabe runs to investigate this and sees Kurisu lying dead in a pool of blood. He runs outside to find Mayuri and sees that a sattelite has crashed into the roof of the building, though the building itself is largely intact. Just as he sends a text message about the situation to his friend Daru, something changes about the world where he hasn't even gone to the conference yet.
Soon after, Okabe (as the "mad scientist Hououin Kyouma!") introduces his Future Gadget Lab (or just "the lab") of fellow mad scientists, which seems to consist of a girl making cosplay outfits (Mayuri) and a fat otaku called "Super Haker Hashida Itaru" (Daru) at his computer. After doing this, he asks about going to the conference on time travel, but a satellite fell on the roof of the building and postponed the conference, even though Okabe has no recollection of what he did in that timeline.
Later, Mayuri decides to get some bananas, while Okabe runs them through the microwave. For some reason, the microwave is turning them into green gel-bananas without actually warming them up.
...and later found alive.
When the conference on time travel comes around at its new date, Okabe drags Daru along with him, and tries to figure out why the world has become slightly different. He discovers that the text message he sent about Kurisu getting stabbed was sent a week ago instead of recently, but when the doors open, he finds himself looking at a very much alive Kurisu Makise.