After years of idly wondering what I was remembering, I stumbled onto a detail from a trip I made once in Japan.
I was backpacking in the early 1990s around Aizuwakamatsu, to visit the castle there. Since my trip was planned by the very helpful people at the Tokyo office of the JTB, they had scheduled all kinds of crazy stops whose purpose I had very little idea.
One of the stops was a country home of some national hero, a famous scientist or other. All the signs were in Japanese and I hadn’t heard of him before, but the guides assured me he was very famous!
Now, years later, this turns out to be the childhood home of scientist Noguchi Hideyo, who discovered the cause of syphilis in 1913, and now has his face on the 1000 yen note.
Mystery solved, almost 20 years later!