Dokonimo Nai Kuni

From Nakama:

For a captain and a subordinate, pure love is born out of an unfeeling time of war, strict rules and order, and a superior-subordinate relationship. Settled in the southern front, a subordinate, Hayakawa, is often punished for causing minor problems by the strict captain, Takeuchi. However there is a secret between the two of them… The war ends, and time passes by. The two return to Japan on their decommissioned ship and decide to live together, but…