Stark, iirc, there is no such thing as a "true" unblockable in BB.
Meaning if two moves, a high and a low, hit on the EXACT same frame, one of them will whiff, unlike GG.
This would mean the best you can do is make the overhead hit ONE FRAME AFTER the low. Yes, basically unblockable, but not a "true" unblockable.
Akiro. Just watch japanese vids. Or pm me whatever combos you're doing now, and I'll tell you where to switch some stuff up.
"What do I work on?" is probably kind of vague for any of us to try and help.
That air combo is fine, though. try and sj.B, because your j.2C whill whiff if you're not high enough for both chars.
Learn j.2C j.C 2D loop and variations. That will be a good start.
Also, learn j.2C Allegretto 8D corner loop and tech traps.