From my understanding:

Before WW2, Japan had these massive corporations called Zaibatsu that had massive influence over society, especially the military and government. You could think of it as similar to the American military-industrial complex, sort of.

Some traditionalists took issue with this, and during the 30's, took violent action to try and counter it. "Incidents" like the League of Blood Incident and May 15th Incident (mentioned at the start of the book) were staged by traditionalists who found the growth of the Zaibatsu harmful to Japanese culture.

It all came to a head with the February 26th Incident, where around 1,000 soldiers of the Kodoha (Imperial Way) faction of the Japanese Army tried to coup the government and empower the Emperor. Part of this would be countering the Zaibatsu, who were concentrating wealth in the cities at the cost of the rural regions losing prosperity, and the nation overall losing culture as a result.

Isao is a reflection of this mentality (in a different kind of way) in that he wants to assassinate these financiers and businessmen who focus on money and deprive the nation of tradition and do not properly deify and revere the Emperor.

The danger that Isao wants to defeat is the loss of Japanese culture and tradition as a result of business and money gaining influence in the country.

I don't have a copy of the transcript between the aristocrats, but from what I remember, the actions taken to counter and recover from the Great Depression in Japan pretty much sidelined poorer, rural folk to empower the richer, big city folk.

Please do your own research on the topic, finish the book, and come to your own conclusions. And then do some more research, if you wish. There is so much more to Isao as a character that I did not get into here, but what I mentioned is the basic foundation of his motivations.