Neku x Rhyme = Maybe if they would talked more and had a better realtion, they could be a real... but they never had a good comunication inside the game so... fail.
Rhyme x Beat = At the start of game, when I didn't know that they were siblings, I thought in they like a couple... I thought they were cute... But... whew... incest...
Neku x anymalecharacter: PLEASE!!! You know that never, never, really, NEVER, you are going to see a couple like this, why? Because this is not an yaoi game!!! You know that!!! They know that if they put a yaoi couple, they are loosing male gamers, so, please, stop dreaming in this kind of pairings!!!
After that, the only posibñe couple that I can see here is Neku x Shiki... and I think they're cute.