According to 'Hikawa seiwa' (Quiet talks at the Hikwa mansion), which is an autobiography of Kaishu KATSU, Izo OKADA became Kaishu KATSU's bodyguard owing to the mediation of Ryoma SAKAMOTO.
勝海舟の自伝「氷川清話」によると、坂本龍馬の口利きで岡田以蔵が勝海舟の護衛を行った。