The role of Mizuno in the D-san action was critical, so it is worth considering his involvement in a little detail in order to understand the influence that intellectual agitators have in the process of the development of labour-consciousness.

He was at Miike in 1959, and he first joined the union when he heard about the violence at D-san. He went to the office of the ‘Old’ union to help organise resistance to split the union into two factions, which was just starting. As a member of the Zengakuren's more moderate JCP-affiliated faction, he thought that he would be able to do more for the union by helping to organise staff within the office than by joining the protest lines. He was studying economics at Tokyo University at the time, majoring in labour relations, and his studies led him to an understanding of the nature of political resistance in Great Britain and the United States. He became one of a number of advisers for the union. In particular, he was interested in the politics of resistance, and the Marxist–Leninist philosophy of workers' rights.

At the end of 1959 a friend who worked in the D-san mine contacted Mizuno and explained the situation there. He told Mizuno that the union was corrupt, and that the miners were being abused by the system of piecework contracts that the company had implemented in an attempt to defray some labour costs. He was afraid that the union would capitulate to demands by the company to accept further decreases in wages. Violence was pervasive in the mine, and the leader of the rbmu was known to be connected with the local yakuza. These were good reasons why the workforce might be compromised.