Well, the story is kinda long, see the condensed story below;

A man who found and reported a lost bankbook claimed 15% of the legitimate owner’s $200,000 bank balance as a finder’s reward, and courts agreed the owner must pay.
The case began when a Niigata prefecture man found a lost bag containing bankbooks, payslips and a legal seal, with the books belonging to an account with an apparent balance of ¥17,000,000.
He immediately reported the find to police, and the lost items were returned the same day to their owner.
Here things began to go awry; the owner of the bankbooks offered not one yen in reward money for the prompt return of the bag, even when asked by the finder – in Japan the “grateful” owner of a lost item is expected to offer a reward commensurate with the value of the lost item or of at least a respectable amount.
The finder soon filed a court case demanding 15% of the bank account’s balance as a reward, based on the owner not fulfilling his legal obligations to provide a reward under the Lost Articles Law.


Japanese law treats the appropriation of lost articles by finders as theft; the legally correct action is to report the incident to police, who will then retain the article for 3 months whilst searching for the owner.
If nobody claims the article it normally becomes property of the finder, except where items containing personal information are involved.
With a generally law-abiding populace, the reporting of lost property is common – in 2009 some 17 million articles were reported to police, 6 million of which were returned to their owners, and 7 million to finders. 450,000 unclaimed articles were withheld based on personal information being present.
This included ¥14,200,000,000 in cash, ¥9,700,000,000 of which was returned to the original owners, and ¥3,800,000,000 to finders.

However, if the article is claimed by the original owner, the law requires the owner to pay the finder a reward, from 5-20% of the object’s value. Failure to do so can result in civil courts forcing a payment if legal action is taken by the finder.
This is a simple matter where cash is involved, but a complex legal issue where many other items are concerned, as their “market value” must be determined.
Mangaka Takashi Tajima, author of several legal manga and a lawyer himself, explains:

“From the perspective of the side losing a bankbook or similar, its effectively a worthless scrap of paper as once reported to a bank it can no longer be used at all, meaning a small reward is justified at best, but the finder is likely likening it to actual cash as if he was criminally inclined he could quickly take it to the bank and make a withdrawal before it was cancelled.”

There have in fact been several high profile cases around just this issue.
In one case in 1983, a bank employee managed to lose a cheque for ¥7,800,000,000. Courts then valued the actual cheque at 2% of its face value, and then ordered the bank to pay a 5% reward to the finder, totalling ¥8,750,000.
In 1991, a lost promissory note was valued at from a half to a third of its face value, resulting in a ¥850,000 payment to the finder being ordered .
Such cases also raise the intriguing possibility that having property returned could actually be far more damaging than losing it in the first place, and more profitable (and legal) for the “honest” finder.
Indeed, it might be less risky for those losing such articles to not claim them at all, since once cancelled they lose all value, and any attempt to use them constitutes a serious crime for which no reward need be paid and liability is generally limited.

These cases are at any rate the exception rather than the rule, a court official says: “Usually these are resolved with a ‘thank you’ payment of 50-100,000. It seems in this case the finder became upset however…”
The case finally concluded with the owner demonstrating that the account in fact only held ¥8,000,000, with the court suggesting a minimal 5% payment – both sides finally agreed on a compromise ¥300,000 “reward.”
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So basically, A guy found B guy lost bags and found a mountain of goodies inside, cash books, bank slips and such which worth $17,000,000yen (yes, B dude is a bloody rich bastard). When A returns the lost stuff to B, he was hoping for some little rewards in return, but B just shove him off without even paying a single yen.

A dude is pissed off and lodge a report to the police (rofl, yea he is pissed) complaining that the B dude did not comply with the Lost Articles Law (I didn't even know there is such thing) where it stated that the owner of the lost item should compensate 5-20% of the object face value. In the end both sides closes the case with A dude getting $300,000 yen as a huge "ang pau".

Personally I have encountered few (many) situations like this before, I found lost money all the time ranging from 10sens to rm8. What I do with it you ask? well, simple... if it was lesser than rm1 I leave it alone, if more then I will use it, if its more than rm100 I would (probably) report it to the police. There was a time when I was just walking through the streets with my friend when I found rm8 cash lying down on the floor. I took it swiftly and looking around for people who might be the owner. None seen, so the cash flows into my pocket..... in the end I use it to treat me and my friends to some good time at cyber cafe, happy ending. XD how about you?