Okane ga nai starts off with a rather typical yaoi fashion but one that has a lot of potential. As it the story progresses, major flaws become apparent and the lack of plot hardly becomes this manga's major flaw.
For starters, there is a complete lack of character development. As many earlier reviews mentioned, Ayase and Kanou's relationship hardly progresses. And it goes a little overboard with the numerous NUMEROUS rapes in the early volumes. Ayase is a little too accepting of these numerous violations with no apparent inner dilemma of any sort. Naivety can only work to a certain degree. Kanou is also obsessed with just being a complete bastard and treating Ayase like an object despite the fact he apparently has feelings for him. Their relationship lightens up as story progresses, especially the latest volume, but it's just awkward and doesn't feel resolved.
I compare this manga a lot to Yamane Ayano's Viewfinder for several reasons. They both contain mafia related elements and both involve rape of uke as the central starting point of the main couple's relationship. However, instead of the "let me be an asshole and rape you because I own you" its a "let me teach you a lesson with messing with me". While the former relationship should have many more issues to work out than the latter, there is a complete lack of this in Okane. On the other hand, Akihito of Viewfinder's character matures into one that ultimately accepts his and Asami's relationship. And Asami, while being a cold-hearted mafia boss that takes advantage of Akihito whenever he feels like it, truly cares for him. He rescues him on numerous occasions and even risks his life for him. While Viewfinder is indefinitely darker and more mature in tone, their relationship is acceptable versus Okane's which has far more comedic moments but just doesn't quite sit right with the reader. (Cute chibis/jokes/cosplaying of rapist/victim just don't do it.)
So please, Ayase, Kanou, get a shrink, work out those unresolved issues that you should have but apparently don't.