I find wallets occasionally in Tokyo and turn them in. Last year or so I found a wallet with $2,000 in Yen. There were ID cards, etc. too. I took it to the cop box and they found the owner. A few weeks ago I found a single, naked, crumpled ¥10,000 bill in the road. I kept that one. I find lots of stuff and turn it in if it can be reasonably identified. I usually don’t want or need the junk anyway and I feel I get the good karma back eventually.
Sounds like you’ve adopted the Japanese lifestyle - NICE!.
In the case of the 10k note, my thought would be to turn it into the police and let them deal with it as a phone call to them within 24 hours asking about a 10k note would likely identify the person who lost it. But even so, that’s not to judge you, just Monday morning quarterbacking.
In the US, it’s so dangerous that I’d likely walk past a $100 bill, rather than try picking it up, regardless of where I am.
Hey I dropped that. Right outside the tower - in Asakusa.