"Otowa" was rushed into service in order to participate in the Russo-Japanese War, joining the Japanese fleet blockading Port Arthur on 16 September 1904 under the command of Commander Arima Ryōkitsu. On 13 December, she assisted in the rescue of survivors from , which had been sunk by a naval mine. In early 1905, she was assigned to escort troop transports ferrying reinforcements from Japan to northern Korea.