In August 1870, YOKOYAMA directly appealed at the gate of Shugiin (a legislative body in the early Meiji period) building with a list of 10 items describing the corrupt practices of those days; after this incident, he committed seppuku (suicide by disembowelment) and died in front of the residence of Tsugaru Domain.
明治3年（1870年）7月、時弊10箇条を挙げた書を集議院門扉に公示し、津軽藩邸前で屠腹して果てた。