The CIA agent is used for the term to identify the general CIA asset, though it sounds strange. The agent is a representative person, such as the lawyer to the organization, or someone internal also being representative, used as FBI agent. In this sense, CIA agent should be an officer working there.
Having said that, the double agent is a meaningful term, who works at the intelligence, but hired as a spy for the other country. In this case, this person is actually an agent at the government, hence it holds the meaning as it is.
Although, CIA agent is used for the term, who is a foreign asset working as a spy, though they are ordinary people, not preferred to be called as such. In this case, the new name is required to work for CIA, which is why the agent is created, while they are basically worthless as a collaborator, informant or others who are actually not happy to be called as the CIA agent, conversely.
Their main job is to steal the economic interest or to control the corporate activity. It is a conduct of the economic spy, but they cannot be openly named as the spy, preferably disguised as CIA agent. There is another field which they are utilized, a covert operation including a conspiracy. It is a crime to steal the critical economic information, though their covert operation is extended to more serious crimes, including a murder.
In the Japanese case, the number of CIA officer is limited, which restricts their capability to affect the whole country. Even if they can obtain enough collaborators within the government, their capability is still limited, so that the black operation is occasionally executed for the deeper conspiracy. Especially, they commit crimes to control the important subject, which is sub-contracted to their assets, hence CIA called them as their agent willingly to work with.
This situation is the same in Europe or even in their own country, the US. They hold their assets to be called as CIA agents, who really believe they work for CIA, but the reality is that they are just used for the supplement or expensed if necessary, as they are in the end, the asset, not secured as the officer.