Setagaya Ward Mayor Under Fire for Allegedly Using Con-Artist Tactics to Build a House

Submitted falsified documents to the authorities

In a quiet residential area of Komae City, Tokyo, four houses sit beyond a so-called “quasi-road.” Three of the houses are standard two-story homes in residential zones with a building coverage ratio of 40% and a floor-area ratio of 80%, each with parking spaces. However, one house stands out—a black mansion that almost fills its 35-tsubo lot, looming over its surroundings. This black mansion has now become a topic in the Setagaya Ward Council.

“Isn’t this house built using tactics similar to those of a real estate swindler?”

On September 30, at the Budget Special Committee’s comprehensive questioning session, Ward Councilor Masaaki Oba posed this question to Setagaya Mayor Nobuto Hosaka (69).

Summarizing Oba’s claim: In 1985, Hosaka purchased an old wooden house on the Setagaya-Komae border. According to the Building Standards Act, a house must face a road at least 4 meters wide with at least 2 meters of frontage. The Hosaka property, however, only had 1.1 meters of road frontage, making it technically a non-rebuildable property. Yet, in 1992, the house was rebuilt.

Regarding this, Councilor Oba accused Hosaka of submitting falsified documents to the authorities, pretending that the neighboring land was also his, in order to obtain approval. At the time, Hosaka was a private citizen and journalist. He was first elected to the House of Representatives in October 1996 and later became Setagaya mayor in April 2011. He is now serving his fourth term.

During the September 30 committee session, Oba pressed further, suggesting that once Hosaka became a public official and aware of the illegality, he purchased land on the Setagaya side with more than 2 meters of road frontage in 2021 to circumvent the legal issue.

Hosaka, meanwhile, was observed closing his eyes, tilting his head to the right, and occasionally looking up at the ceiling while thinking over his answers.

“I borrowed it. There was no deception or falsification.”

Hosaka repeated this statement. Even when Councilor Oba rephrased his questions, Hosaka’s responses remained vague: “I borrowed it. There was no deceiving or falsifying. I did not prepare any promised documents or texts,” leaving the explanation unsatisfying.

A parking lot not directly connected to the house

Hosaka’s residence stands in a quiet residential area, a 15-minute walk from the nearest Odakyu Line station. When our reporters visited, the three neighboring houses appeared standard, adhering to the building coverage ratio of 40% and floor-area ratio of 80%, while the black house occupying nearly the entire 35-tsubo lot stood out dramatically. Additionally, the land on the Setagaya side—purchased in 2021 to balance the frontage, as some point out—has a difference in elevation from Hosaka’s main lot and a wide frontage. Although it is currently used as a parking lot, it is not directly connected to the house, requiring a detour of several hundred meters—creating a strangely impractical layout.

A neighbor of the mayor’s described his impression of Hosaka: “He often returns home looking very tired.”

The neighbor continued: “When I moved here in December 2014, the black house was already built. I don’t know the prior history or what discussions the mayor had with the previous owners. The house was sold at a very low price. When I asked why, I was told, ‘Because it was a non-rebuildable property.’ Despite the concerns, it was cheaper than the market rate, so I decided to buy it. But this area is supposed to have non-rebuildable properties—so how was the mayor’s house allowed to be built?”

Councilor Masaaki Oba, who has been pursuing this issue in the Setagaya Ward Council, expressed his anger:

“The administrative process for building approvals does not involve checking each property on-site. As long as the paperwork is complete, approval is granted. Most violations are discovered through reports from neighbors. Even if a building is illegal, the administration usually issues verbal or written notices to correct the violation but rarely enforces demolition. Some exploit this system, submit fabricated documents, build anyway, and evade accountability—this malicious tactic continues.”

It is difficult to believe that Mayor Hosaka rebuilt with malicious intent. However, the “Certificate of Registered Matters” for the Hosaka property lists the building area as 62.41㎡ and the land area as 233.38㎡. Hosaka’s lot is only 35 tsubo (114.94㎡). Applying the 40% building coverage and 80% floor-area ratio would allow a first-floor area of 45.97㎡, but the registry lists the first floor as 61.26㎡. Adding the neighboring lot brings the total to 233.38㎡. Yet, checking the registry for the neighboring land shows no record of Hosaka’s ownership. Therefore, Councilor Oba’s suspicion—that Hosaka may have used the neighboring property in the application to obtain rebuilding permission and built to the maximum within the lot—cannot be dismissed.

When asked, the Setagaya Ward Council’s Public Relations Division responded:

“This concerns the mayor as a private individual, so the ward office will not respond. It will be handled by the mayor’s office.”

Hosaka’s office replied:

“As stated during the September 30, 2025 Budget Special Committee, there is no fact that the application included neighboring land as part of the residence, and no submitted documents were falsified. The building permit was granted properly.”

Setagaya Ward, home to about 920,000 residents, now has its top administrator accused of potentially falsifying documents to rebuild, with the issue under scrutiny in the ward council. As a former opposition House of Representatives member who has engaged in many investigations, Hosaka may finally explain the matter in person at the special committee session on the final day of the council, October 14.