Though it hasn't got an anime yet, although I hope one day it will, the manga Isekai Tensei Soudouki is pretty much the opposite: The MC, as a native, is just fine and dandy, but he also has two other personalities within his head, reincarnators from Japan. They can exchange information and the reincarnators can take control of the body if needed, but usually it's just the original personality doing stuff, although very heavily influenced by the info and ideas he gets from the reincarnators. However, there's no forceful fusion like in this series and some others, where the MC suddenly remembers (if you can call it that) that they are originally from Japan, typically leading to a strong suppression of the native personality, even if not to a total eradication of it.

I feel like this isn't a spoiler for that other series since it's in pretty much every description of the series out there.