In April 1859, Kuniomi, thinking it high time for Naosuke II's assassination, returned to Fukuoka with Jiro HORI and submitted a petition asking for the upgrading of armaments for exclusion of foreigners and for the support of Satsuma Domain, because if the assassination of Tairo went ahead it would cause a major disturbance.
翌安政6年（1859年）3月、井伊大老暗殺の機が熟したと感じた国臣は掘次郎とともに福岡へ戻り、藩主黒田斉溥へ大老が暗殺されれば大乱となるから薩摩藩との連携と攘夷のための軍備の充実を求める建白書を提出。