On 1859/8/16, Yûsuke met with Mito domain retainers Takahashi Taichirô, Kaneko Magojirô, Nomura Tsunenosuke, Seki Tetsunosuke, and Kimura Gonnoemon, and with fellow Kagoshima domain retainers Hori Nakazaemon (later known as Ijichi Sadaka) and Takasaki Itarô and others at a restaurant in the Sumida area of Edo known as Daishichiro to secretly discuss an attack on Tairô Ii Naosuke. Whether this was their first meeting is unclear, but it was not their last. Yûsuke met with Mito domain loyalists again on 1860/1/19 and 1/27 forming an alliance between their groups, and kept Kaneko in hiding in his own Edo residence for a time starting on 1860/1/25. On 1860/3/1, he met secretly again with former Mito domain retainers (ronin) Kaneko Magojiro, Kimura Gonnoemon, Saitô Kenmotsu, Inada Jûzô, Satô Tetsusaburô, and Seki Tetsunosuke, this time at the Nihonbashi restaurant Yamazakirô, to plan the attack which would take place two days later.
While Yûsuke's younger brother Arimura Jizaemon participated in the 1860/3/3 attack which ended in the murder of Tairô Ii Naosuke, Yûsuke participated only in the planning and was not present at the incident. Nevertheless, immediately afterward, he and his brother sent a letter to Kagoshima officially declaring their defection from their status as retainers - that is, their declaration of themselves as ronin. They then fled Edo alongside Kaneko and Satô, but were captured by Kagoshima domain retainers at Yokkaichi post-station along the Tôkaidô highway on their way to Kyoto. They were then brought to Fushimi, and Yûsuke was sent back to Kagoshima.
Yûsuke committed suicide in Kagoshima on 1860/3/24. He was later posthumously granted the Junior Fourth court rank.
- Ishin Shiryô Kôyô 維新史料綱要, vol 3 (1937), 206, 260-261, 272, 275, 278-279, 284, 287, 290.