Okabe, now thoroughly traumatized, refuses to try again—not wanting to see Kurisu die once more with no hope of saving her. Yet, at that moment he receives a video message from his future self, explaining that Past Okabe had to fail once so that Future Okabe would be created—an Okabe that spent his life figuring out how to save Kurisu and finding the path to the perfect timeline: the Steins;Gate.
Steins;Gate 0 is the life of that Okabe. It is the story of a broken man.
After killing Kurisu with his own hands, Okabe attempts to move on with a normal life. He destroys the “Phonewave (name subject to change)” time machine and all related research, returns to college, and stops going to the lab altogether. The jovial, over-the-top “Hououin Kyouma” is gone and all that remains is a PTSD-riddled shell.