Whetstone

Just an Idea. What If you get a chance to reincarnate with a system that grants you overpowered powers/Items/summons BUT you can't use them for your selfish desires but you need to act as a whetstone for protagonists across the multiverse polishing them so that they can face a vague unknown threat? or be better prepared in their own world. disclaimer: all props/characters/plot etc belong to their original creators. First world: Marvel.