Traveling to Hokkaidō, he became Navy Minister of the new Republic of Ezo, and while he took part in the Naval Battle of Miyako Bay and the Naval Battle of Hakodate Bay, the Ezo forces were defeated, and Arai was placed in prison, where he remained pending a sentence of death.
Traveling to Hokkaidō, he became Navy Minister of the new Republic of Ezo, and while he participated in the Naval Battle of Miyako Bay and the Naval Battle of Hakodate Bay, the Ezo forces were defeated, and Arai was imprisoned, awaiting a sentence of death.