As Cannon Fodder, I Just Want to Live.

There is a huge reincarnation system in the universe, and all dead souls will be sent to different parallel worlds (either to the known history, or to the future that has not yet arrived). Heaven is ruthless, and all reincarnated people will have their memories erased and die young when they are three years old, and the cycle starts over and over again. Only by living older and experiencing more deaths can the soul accumulate experience.