Soukai no Seiki -Ouji to Otome to Kaientai-

In another timeline in history, one where Sakamoto Ryoma was not assassinated in 1867, Ryoma successfully overthrows the government and creates the Naval Support Division. Two years ago, Rinoie Narumi, a young boy, met Saitani, a beautiful naval captain who immediately captured his heart. It is now 1914 and Narumi has enlisted in the Japan Naval Academy and is stationed on the Mikasa, a ship that is now being used for training students. He finally gets reunited with Saitani and decides to stay on Mikasa instead of continuing with the Naval Academy.