Keiichi is a leopard, a predator. Shingo is a housecat, a predator in his own right, but in a leopards eyes he would be prey. Nothing stimulates a predator more than the chase, capture and struggle of prey. Shingo is aware of this because he, himself, is also a predator. He struggles against Keiichi because it makes the sex that much more arousing for Keiichi, which, in turn, makes it that much more arousing for Shingo. Note also, that Shingo usually says "No" to things that will make him, or are about to make him, climax. He doesn't want it to end too quickly. Both men are equally matched in strength, if anything, Shingo would be stronger because of the work he does. If he truly wanted to escape Keiichi's embrace, he could do it easily. So, Shingo struggles, not to get away, but to enhance the sexual tension. The other aspect of this situation is Shingo's tsundere personality. He definitely wants to have lots of sex with Keiichi, but his pride and personality cause him to push away rather than pull close, in spite of himself. Perhaps understanding, or trying to understand, it this way will make it seem less "rapey" and your enjoyment for the story will improve.
You may also be unaware that this type of "rapey", as you call it, sex is actually a common "game" in real life sex. One person will take on the role of the predator and the other is the prey. Some like to pretend they are animals, others enjoy victim/perpetrator roles. Either way, the actions and the results are the same. Things play out just as I described above. Often, the best prey/victims have played the role of predator/perpetrator themselves. They know what is stimulating and how stimulating it is for them and they use that information to create stimulating circumstances when the roles reverse. Frankly, it's a very hot game to play that also builds trust between lovers. Once you entrust your entire self to someone and come out the other side all the better for it, nothing can build trust faster or more deeply.
Many readers here are young and easily influenced by both their ideals regarding how sex "should" be, as well as being influenced by popular ideas in media and social media. If you believe that sex is like it is in fairy tales and movies, hearing or seeing how complicated the subject of sex is in real life can be strange and uncomfortable. Sex is awkward at first, messy - in a good way - in the middle and at the end of the day, even if you're a pro, it is always complicated. I studied sexual psychology while in college doing pre-med and am still fascinated by it to this day, nearly 30 years later. Sadly, the view of sex today is far worse than it was 50 or 100 years ago. Literally, everything, is automatically categorized as rape or sexual assault, even being looked at! Combine that with the tendency for young people to confuse fantasy and reality and the willful dissemination of inaccurate information in order to push a personal agenda, and you have a generation that will enter adulthood choosing to be frigid and/or celibate. The future of our species is looking pretty grim. There is an abundance of information regarding sexual psychology and why people do what they do, like what they like and fantisize about behaviour that would be deemed "socially unacceptable" or looked down upon. However, if it isn't trending on social media, it's true value goes unnoticed. That is why I try to do my little part and educate young people when and where I can. Personally, I love this manga series and I love the relationship dynamic between Shingo and Keiichi. Humans, after all, are animals and it is good to allow and accept that animal part of ourselves, even if it is only in our erotic fantasies and fiction.
"WoMeN RuiNEd Sex WiTH AsSaUlT ClaImS"
I thought I'd escape this enabling crap in a yaoi comment section, but I guess not. Nobody seriously categorizes being looked at as assault or rape, just stop with that false narrative.
Obviously, there are a millions ways to engage in sexual behavior, and consenting adults can do what they want, but there's no reason to sneer at people who prefer stricter boundaries. And anyone who has read yaoi for an amount of time knows that rape and dubious consent are frequent tropes of the genre, so of course they'd be called out.
they're cute but sometimes their relationship has a slightly rape-y vibe to it and i'm a bit uncomfortable.