Steins;Gate Episode 23 - Open the Steins Gate

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. Wanting to save Kurisu, Rintaro travels to the past with Suzuha in her time machine, arriving before Kurisu's death. Witnessing events unfold as they did, Rintaro briefly runs into Kurisu, explaining their prior encounter, before hiding in the room where she will be stabbed. There, Kurisu meets with her father, revealed to be Doctor Nakabachi, who attempts to take ownership of her time travel theory for himself. Rintaro attempts to save Kurisu but 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. As Rintaro falls into despair and refuses Suzuha's offer of a second attempt, Mayuri slaps him, stating that he was never one to give up on someone or something. Suzuha then reveals that Rintaro was intended to fail the first attempt so that the scrambled video message he received on the day of Kurisu's death could be made viewable. This turns out to be a video from his future self, explaining that the key to saving Kurisu without changing the events that led him to develop the time machine and causing a paradox is to fool his past self into believing Kurisu has died.