He should just ask her what's 'Japan'. If she doesn't know it'll just be a weird question. If she DOES know, mc will immediately know from the reaction...
"princess says you have to rest for a week, or your soul could untether from your body"
"alright, now is the perfect time to travel to the capital!"
bruh, your teacher tryin to kill you
Yeah, this kind of MC is hard to come by. He's very kindhearted, compassionate, magnanimous, thoughtful, respectful, benevolent and merciful. He's also not a brute, resorting to pure strength to solve problems or a snake who uses underhanded means to obtain something. It's also great that he shows no excessive impure desires or greed. I really like how honest and upright he is.