I think the reason for that was to depict the difference in atmosphere and experience.
Keith obviously had more experience in sex and is a lot more vulgar, that’s why it was drawn and illustrated in a way where it has to appear sexier and raunchier.
Bunny on the other hand is a lot younger, more considerate and polite, which is why the sex scenes were slightly bland.
Also, you can see how much Kotetsu was feeling it more with Bunny than with Keith.
Kotetsu was more sensitive and adorable with Bunny, and sex, casual, carefree with Keith because he doesn’t like Keith.
Lastly, Keith and Kotetsu sex scenes was also hot because technically, it was kind of a form of cheating or something, not that bad or severe, just the way it felt, so it becomes more vulgar and sexy.
Also, you’re right, the sex scenes wit Bunny and Kotetsu seemed so rushed, I didn’t even feel the love.
And since they’re the main couple, I kinda wished they showed more of them doing it, ‘cause at this rate I feel like Kotetsu would still do it with Keith if Keith pushes the right buttons.
I still don’t have much trust in Kotetsu, even though he’s going out with Bunny now, I really can’t shake the thought that he would eventually cheat on him with Keith.
I like it.
I think sex scene with Keith was much more define and artistic than with Bunny. The only thing I am quite disappointed.