The stone of change, among the vast expanding and destroying cosmos, there exist millions upon billions of different treasures, but for the cosmos, there would forever exist only one stone of change, giving a chance to rewrite the wrongs.
The Law of Time is one powerful element that only a select few could wield even among them none could turn back time. Some might be able to gaze into the unknown past, but none will be allowed to tamper with the true flow of time. The three guardians of the unknown will never allow it, yet they still exist in a way to meddle with what should have been and what shouldn't.
Absolute regression is impossible, Valencia knew it, the stone of change was more like a radar wish granter that lets you choose one path of change. It would let its user one chance to send back a single wish to change fate. The one affected by the stone of change would be under the requirement set by the user.