Japanese summers are notorious after all. I recently read the memoirs of our first emissary to Japan, doctor G.J. Ramstedt from 1919-29, and it has a pretty detailed description of how brutal the summers are.
"Europeans who in the summer try to live in buildings of Western style make a grave mistake. Though the first summer may pass without too many ailments, and by halfway through September the exhaustion from the heat of the summer may have been blown away. But already by the end of the second summer it may take as long as until Christmas that one regains his full health. The third summer may already become critical. I recall, while spending my third summer in Japan, a young Finnish undergraduate Antti Virta from Paltamo arrived to visit me. He was mainly living in Yokohama, but had come to me to complain about headaches and ill health. He also requested me to report to the Japanese authorities that he was by no means a politically unreliable person. When I noted his mental state, which had obviously been caused by the summer heat - he lived in a European style building that had the window right next to the door and he slept in the far back of the room behind veils! - I recommended for him to move to either the mountains or by seaside in some cooler region as soon as possible. But some days after his visit, his landlord came to me to report that Virta had shot himself that morning.
When I mentioned this sad event to an official at the Swedish embassy, I heard from him that around the same time a Swede had committed suicide by poisoning. The ambassador of Norway, when I met him and also mentioned the case, also let me know that a Norwegian had met the same fate, his countryman had hanged himself. And the notable thing was that all three were spending their third summer in Japan."
Thank god for modern AC.