So, I don't ship WeissxNero anymore. I used to, back in the dark days of high school, but I've since realized that it really doesn't make much sense. You'd need to twist quite a few things to make it work. Not as many as SOME of my ships (*cough*Went*ahem*) but enough that I just can't read most of the fic that's posted with those two as a romantic pairing.
I've found that there's a formula though:
Wibbly!Brother + Circumstances + Pervy!OtherBrother = Mansex.
So much is wrong with this.
Who looks at Weiss (or Nero for that matter) and says, "Yep! Wibbly bitch. Commence the uke-fication!" Me and this person need to sit down at a cafe someday. They can order whatever they drink and I will order tea and I will produce fucking pie-charts, bar-graphs, and STATISTICAL FUCKING EVIDENCE proving that Weiss has never been canon-vulnerable, Nero has been vulnerable all of ONCE in DoC canon. And he wasn't even vulnerable then. He nearly killed your player!
Circumstances tends to be nearly fucking anything. "Oh, they're trapped in an elevator..." "Oh, Nero got injected with an aphrodisiac..." (more on that fucker later) "Oh, Weiss is eating a cookie..." I'm surprised that them breathing hasn't been considered an excuse for them to start fucking.
Pervy brother is even more of a stretch for me. I'm of the opinion that unless you're crazy or just that amazing, there is no sex in DeepGround. Meaning, I'm of the opinion that half the Tsviets have retained their sex drive. Shelke is nine and never had one in the first place, Azul simply does not care, and Nero probably never quite had the chance to decide if he had a sex drive or not. So that leaves Weiss, Argent, and Rosso, assuming that Argent cares about sex at all (which I'm having lots of trouble seeing because she's just so damn sensible, but lets assume that she's got libido). In fact, you've even got trouble making a case for Rosso having a sex drive. She's completely bloodthirsty and I'm pretty sure she ate her own uterus (not even close to a canon fact, but I sort of like to think she's that batshit.) So Weiss. At worst, Weiss is the only Tsviet who wants sex. Even then, I don't see him being a royal perv. In AU, sure, but I can make a case for anyone perving in AU (yes, even Shelke. I will write it someday). I don't see Weiss perving in canon.
So, with the fact that they are not weak-willed by any stretch of the imagination, and sure as hell not banging much of anyone, how does this make sense: Nero is injected with an aphrodisiac by DeepGround scientists and then locked, naked, in a room with Weiss, and they bang? How? One, I very much doubt DeepGround scientists keep aphrodisiacs laying around. Imagine how horrible a mix-up with the syringes would go! Two, why would scientists need Weiss and Nero to bang? I was really fucking scared when they brought out the aphrodisiac. This person never tags their stories, and I thought the author was going to have Nero raped (and I'm pretty sure I've seen that before)! But why do they need Weiss and Nero to have sex? I mean, yes, everything in DeepGround tends to be "For Science!" but what science does that show.