Rui goes back in time anytime Trope dies to try and save his life but has failed every time so far. Before Rui became a god, his name was Danchou. Danchou and Trope were together before Trope died and Danchou traded his mortality to try and save Trope. Everytime Trope dies, he forgets who Rui is due to Rui rewinding to when they first met. (Basically Madoka and Homura)