
I don't really get this late trend of getting men pregnant, I mean... It doesn't feel erotic at all, if my boyfriend told me that, I would be fuckin scared

Well, mpreg is a fic kink that's been around forever. As with all kinks, some people like it, some people don't. Some people are really into the male-oriented part of the mpreg kink specifically, and others nosing around in the BL "genre" just want to get their Romance/pregnancy fix on with characters they like who happen to both be dudes. I'm pretty neutral about it personally, although I will admit that some Omegaverse stories would be way worse without the inclusion of this kink.
I'd actually like it if sayu and Asami ended up developing feelings of "more than friendship"