>>AFAIK, the japanese "Coast Guard" is a thinly disguised navy, and they are ramping it up - mostly wrt to countering China.
They're still a Coast Guard, but they're better funded and better equipped than the Japan Maritime Self Defense Forces. They're the better Navy honestly, but I'm pretty sure their Guardsmen do not have protections under the Geneva conventions as the United States Coast Guard does as a Wartime component of the Department of the Navy and as a peacetime component of the Department of Homeland Security.
Much like the Russian Federal Security Bureau (read: KGB)'s Federal Border Guard Service, the Japan Coastguard's employees are civilian government employees from a legal perspective. The thing about this is that in a time of war, civilians who are carrying out Military activity are considered at best Irregulars and at worst, Spies.
Either way there really aren't Geneva Protections for anyone doing that, not that its really mattered since Vietnam (some would say Korea) whether a combatant has them or not. On my Military ID it says I do, but I know beyond the shadow of a doubt that if I'm captured I'm getting tortured, beheaded, or (hopefully) just shot.