The IJN Mutsuki (睦月, namesake: January) was the lead ship of the Mutsuki-class destroyers, which were ordered in 1923 after the Washington Navy Treaty restricted the size and number of capital warships. Due to their nature of being planned as a means for unrestricted rapid expansion of the fleet, names weren't assigned to her class until 1928 after crew dissatisfaction and communication problems. Being an improvement over the previous Kamikaze-class destroyer, she saw service in the Sino-Japanese conflicts, and escorted combat fleets during WWII until her sinking at the Battle of the Eastern Solomons.

IJN Mutsuki was introduced in Update 1.89 "Imperial Navy". She is the first destroyer most players will play within the Japanese tree, and gameplay differs significantly from analogous coastal vessels such as the Syonan. The ship is very much a destroyer geared towards long-range engagements, having the most powerful primary armament and the second-most-powerful torpedo setup among its battle rating, further increasing its performance in gunnery battles with relatively good armour. On the other hand, it has only two, very weak, auxiliary guns and no dedicated anti-aircraft weaponry, making it a poor performer in close-range encounters. Overall, it's a difficult ship to play, posing a number of challenges to a player.