I Have a Fix-It Shop in Another World

According to the parallel-universe theory, the universe is infinite, and almost every universe has a doppelganger of the same person. But there are exceptions to everything. There is a group of people who have only one identity across the multiverse. They belong to no universe, yet can travel between any universes and settle down in them. The protagonist, Wu Fan, is one such person. He opens an interworld agency where people from any universe can hire him to get things done. And so the story begins.