Kurushima and Nojima are gonna perform the Emerald Ri-Maajon
Implausibly young Ace Pilot? Check. Older and Wiser navigator? Check. Pseudo-Romantic Friendship? Check. Can only fly a plane together? Check. There are girls serving the navy since all the men are either on the ground or dead
Why else would nations drafted young women in to their militaries considering the general stance on women in the armed forces during WW2? Its because all of the men have been drafted into the military's ground forces or that they simply died. It would also explain why there are some ficitional ships based on real ship classes, they're just extra ships added since the previous ships have sank. The Unbei itself is said to be have converted from a civilian ship so that also supports the theory. Kuki knows all about Miyama's crush, but she's an oppurtunistic teasing sadist.
Even by the strange standards of the manga, it's still pretty hard to justify Kuki's complete ignorance of her first officer's crush. Rather, she's all too aware of it, and uses every chance she gets to make Miyama squirm (similar to Ann and Mary, only far more subtle). From teasing her about sharing a fruity drink together (and catfishing her twice about it), to stripping down in a FREEZER to have an excuse to huddle near her, to promising her "anything you want" if she beats her in judo. If you look at it carefully, it starts to look less like ignorance and more like spur-of-the-moment torture.