I thought it might be a Blackline after some googling. xD
The blackline is so much more active though, and spars with every single rasbora in there. I'm pretty sure I only have one or two females too. He chases the females around almost obsessively. I didn't expect such behavior so soon.
Charlie: No nipping from the Rasboras yet, a few have gotten close to him, but are very quick to flee when he begins moving.
As for the betta, there has been some chasing, unfortunately, but the rasboras have no trouble getting away. The chases usually only last a couple seconds, and he usually only does it when they stray towards 'his' castle.
When the lights are off though, the rasboras seem to go into a zombie state, and no longer pay attention. I watched one swim right into the bettas face, and it got nipped, and is now missing a part of its tail fin. Poor thing, it doesn't seem to be having any trouble getting around though.
Though, like I said, my rasboras aren't even fully grown. They're only about 0.7 inches. I may start floating my betta in a cup at night until they grow a bit. You can try with yours, and watch the results carefully. If he's too aggressive, then you can take him out, and try rearranging his decor. :3