C'mon Japan if you're dealing with the korean association chairman who's a former S rank you can't just send some scrawny ass who's easily intimidated, even if he's your assoc chairman
Warfarin is the usual long term anticoagulant used for patients with valve replacement. Idk about other countries but it should be cheap and readily available. However, those taking it need their INR and PTT regularly monitored so facilities for that in NGOs may be limited or none at all. Maybe...
It's a Japan problem, or I would even dare say that it's a first-world problem that there are too many doctors to give them all experience. Third world countries usually don't even have enough doctors to serve the population, so the system needs every intern or resident they can get to throw...