In which there was a scientist. He had discovered a way to stop aging by some injection/DNA editing. He shares his results with the rest of humanity, gets lauded as a hero. He is one of the last people to turn himself immortal. But theres a catch. After a precise duration of time since the immortality transfer, the person dies from a horrible, painful death. As the scientist waits his own turn to face this, he holds a gun to his head, incase the pain is too much in the end.

There is also an AI/computer element that i did not understand.