Star Ember: I Am a Legend

In 2049, humans captured fragments of the Singularity that escaped from the edge of the universe, and discovered that the Singularity energy can reverse the human body's dying state and repair innate genetic defects. However, there is an irreversible contract: the guardians who accept the Singularity transformation must personally kill each other when the redeemed come of age, otherwise the Singularity will go berserk and swallow up the entire city. The government has blocked all experimental information, and all the modified people and experimental family members have been included in the secret observation list. No one knows about this cosmic transaction hidden under ordinary life.