In 1925, Matsumoto assumed the office of National Levelers Association (全国水平社, Zenkoku Suiheisha) as chairman of the committee.

Having strong ideas about equality between people throughout Japan, Matsumoto organized the resistance of not giving the title of nobility [clarification needed] to Iesato Tokugawa.

In 1948, being a vice-chairman of the House of Councilors, Matsumoto made a refusal to the Emperor's audience in the case known as "The Sideways Scuttle of a Crab".

During Matsumoto's stay in Dalien, he worked as a quack doctor under the title of "first class army surgeon of Great Japan".

[3] In 1942, when Matsumoto had won a nomination to Taisei Yokusankai, his campaign bulletin had the following greetings: "Streams of blood for the Country!

", "Overthrow America in the fight 'til death, destroy the Anglo-Saxon domination of the world; in unity of hundreds in one nation, the young and the aged united in gunfire, despite hardship, leading to invincible victory!

[6] The creeds of "Eight Days Committee" were used during the early beginnings of the Pacific War: "Let our every action show the real meaning of the national polity!

Though Matsumoto did everything he could to support Japan's war efforts, including budget agreements,[7] after the defeat he suddenly shifted to the side of opposition and rejected militarism.

[9] In January 1953, in Yangon, Burma, at the welcoming citizens' mass meeting, Matsumoto delivered a speech as a representative of the (leftist) Social Democratic Party.

He said "Japan is now a rapidly developing and economically growing country, but on the other hand, it came at the peril of imperial fascism.