One small similarity note about Stellvia and Vandread is that both offer a tandem crew arrangement. Moreover, both offer a lovebird crew.

My Vandread screenshot library is lacking.

I've read about female gunners flying Il-2 in WWII with objects of their affections. As far as I know, the practice was discouraged, but it's difficult to find good accounts. Considering the mortality of Il-2 gunners (7 times that of pilots), if a pilot were to return the feelings, he would have to object to further assignments, with consequensies fanning from there. One pair mentioned above was buried together after their plane was downed with a hit from AAA, so at least there wasn't any extra survivor angst.

Closer to now, I recall reading about a husband and wife flying AH-64. There were articles in glossy magazines like Newsweek, with journalistic vultures digging into possible issues.

Stellvia and Vandread do not make a big production of any possible conflict of interest. In both cases, flying separately provides ample of opportunity still. There's also no intrinsic assimmetry such as on Il-2.

UPDATE: My Squadron-Signal publication on Il-2 says: "A number of Assault Aviation Regiments had female rear gunners, such as the 804th Assault Aviation Regiment which served on the Kalinin front in May of 1943."