Meikyuu Kingdom: Damu Tokushu Butai SAS no Ossan no Isekai Dungeon Survival Manual! - Vol. 1 Ch. 1.1

[xanon]

If anything, it seems like the costumed weirdos was trying to kill him before he got isekaied.

Unrelated: Does the SAS even accept Japanese citizens into its membership? Wouldn't they worry about their loyalty, the same way the CIA doesn't really have non-Americans as anything other than assets?

Maybe if he was a UK citizen born in Japan, maybe a dual citizen? He'd have to clear some serious security screening and be uniquely talented (which, he's the MC, so of course he's extremely talented).

That said, there is a zero percent chance that he'd get exposed and be out of the service in a month. First and foremost, you can't just leave a service like SAS like that - this isn't like deciding to quit a regular job. SAS would also have a vested interest in keeping him around - he appears to be a trained covert operator, they would have invested a great deal of money in him so using him as cadre if nothing else. Then there are the security risks to just let him waltz out of country. And, there's no way his debriefing and investigation into his exposure would take less than a month.