The brutal scenes between Taki and Klaus are a little like that, in the sense that Taki is specifically choosing not to give an alternative signal that, according to Klaus, Klaus would take as "no". In BDSM you choose a specific word or signal: typical rules for "no" and "stop" don't apply. However, I think it's useful to consider the ambiguity some people see from a perspective of BDSM.
After all, rape is rape because one party says "no" and the other party doesn't stop-having had consensual sex in the past, loving each other, or being really upset doesn't change that fact. It's definitely abusive, and it probably is rape. Some people are turned completely off for good, others try to defend it as not rape. Other commenters mention the rape scene(s), and for good reason. This isn't straightforward or lighthearted. (I say that as someone who typically rolls their eyes at angst.)
It's a major part of the plot, but it's interesting and adds just the right sort of angst. My sweet spots with manga tend to be pretty specific, and war/military ones (while I don't unilaterally dislike them) aren't one of themes I specifically seek out, either. And so much to sink your teeth into psychologically. This is an absolutely gorgeous, fascinating, engrossing manga. Inariya-sensei!! Please come back to us!!!! We're gonna die!!!! (Oh God, just don't make it happen, please!) That this could have a very/not so impossible tragic ending. Only one thing I am deeply bothered about this series/manga. That the saying, "Love knows no-." could be for real. That Klaus and Taki' s love for each other was so powerful that no boundaries could ever tore them apart, that "LOVE" can truly conquer everything. That this term is greatly more than word itself. This also made me realize how powerful "LOVE" is. I have re-read the manga more than twice just to deeply sink my fujoshi brain into the complicated yet touching story of Maiden Rose. I LOVE the story, the art, Klaus, Taki, the other characters/nameless characters and even the wisteria/flowers and the tanks and train. The art is so beautiful/breathtaking that I could keep a portrait of Klaus and Taki on our wall.
BECAUSE OF KLAUS AND TAKI.I COULDN'T TRY TO READ ANY OTHER YAOI SERIES ANYMORE!!!!!!