Steins;Gate

Synopsis

On the roof of the building where Kurisu was killed, Suzuha explains that her mission is to prevent Kurisu's death and enter a world line known as Steins Gate, in which World War III never happens. Okabe reluctantly travels to the past with Suzuha to just before Kurisu's death. Witnessing events unfold as they did, Okabe runs into her (explaining why she claimed to have met him 15 minutes earlier when they first met) and then hides in the room where she will be stabbed. There, Kurisu meets her father, revealed to be Doctor Nakabachi, who attempts to take ownership of her time travel theory for himself. As Okabe attempts to save Kurisu, he inadvertently stabs her himself, allowing Nakabachi to escape with her theory to Russia, an event that will lead to a time machine arms race and eventually, World War III. Returning to the present, Okabe falls into despair and refuses Suzuha's offer of a second attempt. As he attempts to leave, Mayuri slaps him and tells him that he was never one to give up on someone or something. Suzuha reveals that Okabe was meant to fail the first attempt so that the scrambled video message he received on the day of Kurisu's death could be made viewable. It turns out to be a video from his future self, explaining that the key to saving Kurisu without changing the events that led them to develop the time machine and causing a paradox is to fool his past self into believing Kurisu has died. (Source: Wikipedia)