Immersion is an ability which allows one to cross the boundary between fiction and reality and enter the imaginary locations depicted in books, paintings, movies etc. The places and time periods accessed through this ability are conceptual, as in they do not exist in reality, but users of this ability can still interact with and explore them like they can any place in the real world.
Examples of Immersion would be jumping through paintings into the worlds displayed on them, entering a book and becoming part of the story, and so on. Users can use this ability to retrieve weapons or other useful tools from fiction, evade attacks by entering these other fictional worlds, or use them to BFR or seal opponents. In many cases, users often need a medium that displays their target location as a gateway.