For those of you that think "standard harem isekai shit", that's how it usually goes, either way. Misunderstandings, OPness, SASUGA MC-KUN moments, all that. At least the art here is good.
If you want an story about an actual background character who stays background (and for it to be interesting), it would have to be something like the story of HUNK from Resident Evil. Guy is literally called Mr. Death, has survived Racoon City and he can literally OHKO mid-boss level zombies with his bare hands (though this could be considered non-canon) yet he remains a normal mercenary, doing normal mercenary stuff.