Jimi na Kensei wa Sore Demo Saikyou desu - Vol. 10 Ch. 86

[YamiRi]

wow another Japanese
so many Japanese got isekai'd in this series

 

[AquilaSilvestris]

wow another Japanese
so many Japanese got isekai'd in this series

I think I've only read two series where any non-Japanese get isekai-ed.
In neither manga are they the main (or even important) characters.

Spoiler: In the first case...

there's mention of a reincarnator in Kamitachi ni Hirowareta Otoko who misunderstood old Japanese samurai culture, but spread it to an otherworld tribe anyway.
By the time the story starts, the guy's already long dead.

Spoiler: In the other case...

Gokufuri Kyohi Shite Tesaguri Start! Tokka Shinai Healer, Nakama to Wakarete Tabi ni Deru starts with some god kidnapping a whole bunch of people from all over the world, but the story only follows one (Japanese) person as the MC, with a few chapters from time to time following up on his (also Japanese) friends who got isekai-ed to the same world.