There are a few issues with having introduced a proper rival. While it would've been fun, I would have felt the need to bloat the game with even more scenes to justify it, and I can't guarantee these scenes would've been any good.
I planned out most female characters with Kendo in mind as well, and pairing them with yet another dude wouldn't have felt as good (which is one reason why I haven't paired Arato with, say, Natsuki or Erina).
And then there's the fact that the story would've had to shift to a focus in which these men competed for the women, something I'm not interested in.
I understand your point. For sure planning a whole scenario and putting at some point some kind of twist must be hard to properly arrange it.
What I really liked is all the confusion in the main characters (Kendo, Mary, Satoshi). Satoshi who doesn't know if he is up to the task as a boyfriend, is really insecure and express it by being a dick to his uncle. Mary who tries to be the good faithful and respectful girlfriend but can't help but be appealed by the virility of Satoshi's uncle. And Kendo, who is very understanding and caring with his nephew, but can't help lusting about his girlfriend as she saved his [sexual] life.
However, what I found disturbing (I wouldn't say dislike, because don't get me wrong, you made one hell of a good game), is how they have nothing to do anymore with their original character.
Kendo became really arrogant really quickly and even enjoys cucking his nephew. Mary is head over heels of Kendo's dick as she can't deny she is a size queen. So much she pretty much became the tout of the pimp. And Satoshi who is just "there" looking.
The rival would have made the things more complex (and more complex to implement I recon). Like introducing him right at the beginning after the first sex between Mary and Kendo. Like someone knowing Satoshi and using it to blackmail Kendo and Mary (but well blackmail isn't up to the taste of anybody).
Or later, once Mary completely fell under kendo's attraction, a rival who has traits that Kendo's doesn't have, hence attracting Mary. And an acquaintance of Satoshi (to keep making him "relevant" in the story), like a way for Satoshi to have a revenge on his uncle.
Anyway, I'm sure you probably thought about this thoroughly. This is just my own opinion.
Keep up the good work !
