Plummeting approval ratings and defections by political allies ultimately persuaded him, however.

The amounts that Mr. Masuzoe has been accused of spending improperly on himself and his family are hardly vast by the standards of modern politics-and-money scandals. There are reimbursements of a few hundred dollars here for restaurant meals, and a few thousand dollars there for hotel stays.

In a report issued this month, lawyers hired by the governor to review his spending found 4.4 million yen, or about $41,000, in expenses over several years that they called “inappropriate, but not illegal.” Mr. Masuzoe apologized and said that there had been “some mixing of public and personal” in his spending, but that he had not knowingly broken any rules. He has not been charged with wrongdoing.

Still, the relatively minor scale of his reported excesses did not help him.

If anything, the public’s antagonism appears to have deepened. The word that has perhaps been most frequently used to describe the episode is sekoi, meaning cheap or petty. That Mr. Masuzoe might nickel-and-dime taxpayers and contributors for spa trips seems to have struck a rawer nerve than if he had engaged in wholesale theft.

“I’m angry. This is sekoi — too sekoi,” Shigeru Kamibayashi, a member of the assembly from the right-leaning Liberal Democratic Party, where Mr. Masuzoe has spent most of his political career and which supported his bid for governor, said after the lawyers issued their report. The word has been ubiquitous in newspaper and social media references to the scandal.

Among the spending that the lawyers labeled inappropriate were purchases of manga comic books, some worth just a few dollars, and a silk calligrapher’s robe from a Shanghai tourist gift shop. Mr. Masuzoe charged them to his campaign organization, which by law is supposed to finance only political activities, though experts say the definition is vague enough that politicians routinely stretch it to cover private expenses.