Arc System Works and 4Gamer have published a video where they show off the two new characters Naoto and Hibiki. Even though it's all in Japanese, there's still a lot to be learned about how these characters work.
It is not necessary to get black balls to enhance BRO. Regular balls can enhance it. The fastest way for that is just set then BRO.
If you want the fastest way to get a black ball:
Set > CR or SA
QV > CR or SA
Holding 2 ball then releasing is easier to charge but slightly slower
YRCing can give a lot of black ball possibilities
But because you want black ball into BRO. I'll say just a regular set or QV then CR or SA
However, the opponents pressure is situational and matchup dependent. You don't need to directly make a sequence. You can move or wait then complete