The number of CIA officer is not enough in Japan to conduct a large-scale political operation. I am not sure how many of them are active in Japan, but it is highly likely a couple of hundreds including undercover agents. Moreover, the number of agents are by far lesser who can speak Japanese, which is actually quite critical for the electromagnetic manipulation.
This technology uses a human brain to read the subject’s mind or to send a thought to them. If the operator does not have enough command of Japanese, they cannot conduct these operations against Japanese, or it might be revealed to the subject when using imperfect Japanese.
At the same time, Japanese dialects are strong for many regions, hence it is necessary for agents at least to understand its locality, which implies it is nearly impossible to execute the electromagnetic operation just by the CIA officers. They need to hire and maintain assets for this operation as well.
Five Eyes are functional as well in this occasion, as they can expand the asset base to conduct a covert operation and also they should find more appropriate spies to run the specific operation.
Not all of the CIA asset is involved in the electromagnetic operation, but there are many people maintained as an asset by the agency. I was actually told to watch out the car accident and it is effectively used to hire the subject as an asset. I know some of them, but it is partially understandable as it should be quite hard to go away, if harming others. It might cost too much and might cost a jail time as well, which was why they decided to take that choice. There are also various ways to frame the subject to hire as an asset of the intelligence organization.
Fundamentally, there is no connection between each asset and they can just conduct their part of the operation commanded by the handler, but they basically confirm each other whether they are spies or not. They can make themselves understood just by way of communication which can only be recognized by assets because there is a common knowledge which they just understand what it means and not for others.
I was talked to in that way by tens of them, which I did not understand what it meant in those days when I had no idea of spies and assets. It also means I know tens of CIA assets personally, as I have been a target of them for a long time, but never been fallen to their plot at least for criminalization.
There was one critical issue during a conversation with them that one of the CIA assets knew the Japanese finance minister, Shoichi Nakagawa, was assaulted by the electromagnetic operation. This conversation was held days later when he was dead, but I did not understand what this spy mentioned at that time. However, I remembered something strange at the wording, which implied the incident was a conduct of the electromagnetic wave manipulation.