However, Kongou's sisters all call Kongou "onee-chan". We never ever hear Mutsu refer to Nagato as her "onee-san" or "onee-chan", nor does Nagato ever refer to Mutsu as her imouto.
So while Hiei, Haruna, and Kirishima are all a bunch of siscons, I don't think we can really apply that label (or the incest label) to Mutsu and Nagato.
Roosterteeth has sold specifically bumblebee ship merch and their VAs and plenty of staff openly ship them yet the most official shit is yang liking blakes new hair. As for ruby and Weiss they have even less official sustenance but maybe Weiss’ mom has a chance
^In my experience half the time they do that they don't actually understand the first thing about the relevant topic(s) and the result is worse than just handwaving it... "Artists Are Not Engineers" as it were, and most seem quite lost on even something so basic as how ectothermic ("cold-blooded") metabolism functions in practice. (You run into that an awful lot with reptilian-themed critters because obviously scales = ectotherm amirite guise?)
The audio story has many advantages, such as not having to stare at the monitor. And it's a good option for those who have a high probability of being caught doing something important. The first thing outsiders will do is look at what's going on on the computer...check it out. It's also handy to keep things like that on your phone and carry them with you. I'll tell you that I like audio porn more, many times more exciting than https://www.nicolebdsm.com/east-london-mistress/ videos. I honestly don't know why. I press my player button, close my eyes, and run my hand between my legs. And I start caressing myself.