When I was in Tokyo in 2017, I left my daypack in a taxi. I asked the person who was running a cooking class I was attending if there was anything I could do about it. He made a phone call and within an hour the backpack was returned. This article in Mental Floss explains why it's so easy to recover lost items in Japan. The reason is that large cities like Tokyo have lots of tiny police stations, called kōban (交番) in every neighborhood. People who find purses, wallets, etc., take them to the nearest kōban. Here's how it works, according to Mental Floss:
In 2018, 4.1 million missing items were turned in to police, and the chances of reuniting them with their owners is pretty good. That same year, 130,000 of 156,000 lost phones (83 percent) were returned and 240,000 wallets (65 percent) went home.
Missing items are typically held at the local koban for one month in case the owner retraces their steps and comes back. After that, they're sent to a Lost and Found Center at the Tokyo Metropolitan Police Department, where the item is cataloged, searched for information relating to its owner, and then put into an online database that the public can check. Belongings are held for three months. After that, they might be handed over to the person who found it. If not, they become the property of the local government, where they might eventually trickle down to secondhand thrift sales.