WARNING!, Spoilers Unmarked!
The horrific consequences of time traveling no matter what everyone's dilemma is.
When Okabe sends a mail to Daru on his phone after discovering Kurisu's corpse in the Radio Building's storage room, he suddenly shifts to the Alpha attractor field as the mail was sent back in time thanks to the phonewave. Upon realizing that the phonewave could potentially be a time machine, they conduct experiments with it by asking their fellow labmems to use their mails on their phone to send it back in time and Kurisu also modifies it to become a time leap machine.
But while to the benefits of others; Okabe himself, Faris, Luka, and Moeka changed the past to solve their personal problems, it also brings horrific Trauma Conga Line to Okabe when he witnesses Mayuri's death with his own eyes and tries to save her with his own hands by using the time leap machine but despite how much efforts he put into it, Mayuri will die no matter what because it's the Alpha attractor field convergence that will always pre-determine Mayuri's death into play according to Suzuha who reveals herself as John Titor, the mysterious time-traveler who came from 2036.
Suzuha reveals that in this attractor field, there is even a horrible conflict after Mayuri's death with the Bad Future where SERN monopolizes the time machine which Okabe, Kurisu, and Daru built so they can convert the whole world into a dystopia; stripping everyone of their free will while culling some of them if they disobey their rules. Okabe understands that to avert Mayuri's death convergence, he has to undo all of the D-mails that most of his labmems sent.
While we had so many conflicts in our past that brings grief and sadness, we realize that we mustn't change the past not only it will cause an apparent time paradox but also because the conflicts can define us who we are currently as they serve as a great lesson when we started from birth through childhood until now.
