Mob Protagonist
Tag to be used in a variety of situations where the main character assume the role of a unassuming/unremarkable/side character:-
1. The main character transmigrated/reincarnated into a fictional setting that the main character knews (video games, light novels et. al.), as anyone (a major character, a minor character or even an unknown) but the fictional main character him/herself.
2. The main character transmigrated/reincarnated into a fantasy or parallel world as an extremely ordinary character, such as the member of a lower ranking race of the said fantasy or parallel world.
3. The main character starts right away as an ordinary character of a fictional non-Earth world.