I am of the opinion that ANYTHING can happen in a fantasy. Especially a drawn one (such as manga and comics), but I take an issue if someone seriously thinks that climaxing while being raped counts as consent. It doesn't. It's actually a common thing that women and men have experienced.
I'm not here to whine about rape happening in manga, but statements like yours can be seriously damaging and are also one of the reasons why the fujoshi/fudanshi community (a.k.a Bl fans) has such a bad reputation and is even despised.
I'll just make it clear, that I am not seeking to fight with, or to scold you. What I am trying to do is give you another viewpoint and make you think about it a little.
If you didn't think there was rape involved in this manga then why did you even bring up your point? "It's not rape if s/he likes it" what is the point in bringing up a topic that has nothing to do with the source material? If you DID think this was rape at first, the uke literally decides to let the creep fuck him for the money, if you noticed during the first sex scene he gets a little overwhelmed and then says: "but what about the 10,000 yen per hour" in his head. Also, as stated above the uke DOES indeed tell him to put his dick in and basically seduces the creep because he's (the uke) feeling so good. I don't think it was rape so much as shock in this case, the uke was just shocked for a bit then decided he's okay with it.
I actually love this (≧∀≦)