Rintarō Okabe is an 18 year old mad scientist who has 2 friends who help him out in his mad scientist tasks. Okabe and Daru are rather smart, with Mayuri not-so-smart.

Okabe is pretty crazy, such as talking to himself, and making it clear he's a mad scientist. He's pretty much a dumbass. Kurisu is a fellow (famous) scientist girl he meets in the first episode which offers a huge amount of foreshadowing, as Kurisu dies shortly after he meets her, then he texts daru. Immediately his brain goes crazy, which signifies that the timeline has split. He is (as far as we know) the only person who can remember everything from timeline to timeline. Later we find she is not dead.

Rather inexplicably they have made a microwave controlled by a cell phone which does not actually cook food. Instead it sends something back into the past. Anything inside the microwave gets sent back in time, but loses its chemical composition and turns into green goop. Much simpler things, such as 39 bytes of data, can be sent back to pagers/cell phones.

The first few episodes detail how they use the microwave time machine to send messages (D-mail) into the past. They gain new friends, find out more about the problems associated with sending dmails, and get themselves into a horrific mess.

The other thing that is developed is an actual time machine, which a person enters, and is sent back in time, along with the machine itself. It can only go backwards. The third method of time travel is using a huge amount of suspension of belief (compressing 2 TB of data into 39 bytes) and sending memories back from a cell phone, transmitted directly into the brain, with a limit of a few days (otherwise the difference in memories would be too great). This is called a time-jump.

Since Okabe is the only one who can remember things after a d-mail (it's uncertain whether or not others can remember a time-jump, as he's the only one who has done it), it's very confusing to both him and the viewer.

Why does John Titor visit the year 2000?
How does Ruka become a girl without becoming a completely different person? The sperm has to be a completely different sperm. I can understand that even the slightest change in ruka's mother's daily life would alter the rest of the day, and thus the act of procreation later. Of course if she sent the D-mail when her mother was pregnant, then that's completely insane.

Okabe (the tall guy in the lab coat) is an electronics student and friends with Daru (the fat one) and Mayuri (the girl in the hat). He plays the persona of a "mad scientist" who's persecuted by an imaginary Organisation.

One day, he goes to a lecture about time travel and meets a brilliant young physicist called Kurisu (the red-hair girl with a tie). She mentions they've met, but he has never seen her before. Later, he hears a scream and finds Kurisu lying in a pool of blood. When he sends a text message to Daru about how she was murdered, he finds himself in a weird world for a while. Then, he discovers history has changed: the lecture he remembers having attended never took place, and Kurisu is alive.

Eventually, Okabe and his group of friends, to which we add Kurisu, Suzuha (girl in pigtails who works in the shop of Okabe's landlord), Moeka (tall silent girl with mobile phone), Ruka (guy who looks like a girl and dresses like a shrine priestess) and Feyris (cosplaying cat-girl) discover that somehow, the phone-operated microwave they've constructed can send stuff into the past. Organic matter gets turned into jelly, but data, like short text messages, can travel back just fine. Okabe realises that the message he sent to Daru about Kurisu's death was sent into the past, as well.

Okabe and his friends send a number of text messages to the past (called D-mails) that change history in a number of ways, although Okabe is the only one who remembers there ever existing other timelines. At the same time, the group has done two more things: First, they've hacked into a research institute called SERN, which they were only able to do thanks to a rare, old PC called IBN-5100. They found that SERN has been studying time travel and done several human experiments, which resulted in deaths. The IBN PC vanishes from the lab when Moeka sends a D-mail. Second, Kurisu has somehow managed to find a way to compress the memories of a person into D-mail size, creating the "Time Leap Machine". By sending a person's memories back in time in the form of a D-mail, it's like the person themselves travels back. However, the machine has a limit of two days; any further and the past and present brain are too different.

SERN discovers Okabe's group has been researching time travel and wants to stop them. After sending threatening messages to Okabe, they end up raiding the lab. At this point, we find out Moeka is a SERN spy. Moeka kills Mayuri, but thanks to Suzuha's interference, Okabe is able to leap into the past. Although he tries several times, he can't prevent Mayuri's death; even when they evade SERN, she dies in some other way.

At one point, Okabe is approached by Suzuha, who reveals herself as a time traveller from 2036. In the timeline Suzuha's from, SERN rules the world with an iron fist. Suzuha's original mission is to travel to 1975 and get an IBN-5100, but she stopped in 2010 to try and meet her dad, which is eventually revealed to be Daru. Suzuha finally travels to 1975, but the group later learn that her damaged time machine caused her to lose her memory from 1975 to 2000. Distraught, she committed suicide one year later. Okabe realises that he is the one to blame, since one of his D-mails delayed Suzuha's departure until after her time machine had been damaged by a storm. When he reverses that D-mail out of guilt, he finds out that, as a side effect, Mayuri's death happens one day later than usual. From this he theorises that if he manages to reverse all the D-mails that were sent in the first half of the show, maybe he can reach a timeline where a) Mayuri doesn't die and b) they have the IBN-5100, which will allow them to hack into SERN again and delete all the information they have about Okabe, preventing them from ever attacking.

So far, Okabe has managed to reverse Feyris and Ruka's D-mails, even though both of them were happier with the new timelines. Now, the only message that remains to be reversed is the one sent by Moeka...How will Okabe be able to persuade the SERN spy?

From what I've understood, in every time line, people have their own memories which are not linked to each other and don't affect one another. BUT those who have send D-mails can remember memories from that time line (in which they have send it) and the trigger is Okabe. Maybe because of the Reading Steiner? Other than this, there's no exceptions. But yeah, it would be nice if they explained why those persons remember sending D-mails.
Sorry for possible grammar mistakes

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