There are many Japanese assets of CIA, ranging from spy, collaborator, informant and so on, but they definitely help the intelligence to gather the information or to execute the political plot. They are not officially hired by CIA, as they are a Japanese citizen, foreign to the agency, who are conducted by their handler, the CIA officer. Although, CIA is not the only intelligence active in Japan which keeps Japanese assets for their plot, mainly hired by European countries, but also by the neighbors. Actually, Japanese neighbors hold many spies in Japan, though Five Eyes are big enough as a total to execute any operations in Japan. These countries collaborate for the intelligence including the asset operation, which is likely a consequence that the US utilizes the asset acquired by other members of Five Eyes.
One serious question is why there are many Japanese becoming as assets of foreign agencies. It is quite less likely for Japanese to work as a spy for the other country, but it happens as the intelligence agencies acquire some from criminals or the people losing the future direction. For example, a foreigner commits a crime in the US, who is assumed to be worthwhile for CIA operation, then asking a deal to lift the legal charge if working for them. It should be applied, when someone is stuck by the criminal organization, that CIA should help them as a barter working as a spy.
The intelligence conspiracy is evolved from here to have someone as an asset by way of criminalizing or involving to the illegal activity. If the agency really wants to obtain this person, they frame the target fallen into a criminal, who is eventually presented a choice either the jail or the asset.
The more unacceptable plot is a car accident, which is set up by the spy, obliged to pay for the charge and compensation, otherwise becoming an asset to CIA. I am personally acquainted with some of them and was also nearly fallen to the plot, but this is a dangerous issue to the US as well because the incident has killed the US citizen as a result. They can frame the accident, but cannot control its degree.
Japan has the own issue related to it, as the Japanese police knows this framing and realizes the people working as CIA assets, but they are deterred from any actions. One of the reason is a give-and-take that they are necessary to leave away from the CIA issue. To make the situation worse, some of ranking members of the police department are CIA assets, especially of the intelligence division. Some of them have reached to the director general or the director of the intelligence division.
There are several reasons why the intelligence officer becomes CIA asset, one of which is basically the same as how other individuals become assets, to be involved in the crime. Or, there should be the case that they are willing to become one of them, as they are well informed from CIA. In that sense, some of them actually do not realize to be an asset, unnoticeably to provide the intel about Japan.
The information sharing should be required as one of the allies of the US, though the issue is that the conspiracy is also executed in this scheme, which drives Japan to the wrong direction. Japanese intelligence is apparently capable to run the political plot which is not operated for the country, but to undermine the Japanese society.
These spying activities are not just operated by the intelligence and police, but also done by CIA assets, broadly existing amongst the society. I know tens of CIA assets, but anyone of them is not willingly to become an asset, but they are driven to, mainly by the framing. This situation holds true to the assets held by other than Five Eyes. I still do not know why CIA would like to expand their spying capability to the ordinary people, though it is a reality that there are more assets than you can assume.