Gate: Jieitai Kanochi nite, Kaku Tatakaeri, Re:Creators Recommendations
Both have main characters crossing worlds and being confused about it.
Re:Creators has a really original premise: fantasy chars appear in modern Tokyo, not knowing they were watched by Otaku as anime/game characters, and now have an opportunity to find their writers and animators and beat them to a pulp if they want; one young otaku gets an accidental prime spot as an improvised "Japanese host" for the girls (after some sketchy events ofc), then a plot appears and there are fights between those characters everywhere!
Gate has the Japanese SDF cross a gate to a fantasy world, face its armies and after
In both stories the anime/other world bacomes reality. The people from the anime/other world as well are the people form the real word fight for their beliefs. Both male MCs like very much anime/manga/light novels and also like to come in contact with the people for the anime/other world.
Both have the same plot where powerful beings from another dimension comes to another world where they have established themselves as the superior ones, however , in Gate it involves humans coming in from a portal that connects to their world to the world of fantasy , in Re:Creators in the other hand it was a complete reversal, where it involves, the works of man coming to life and establishing themselves into the real world.