I use Benimaru a lot, actually. He’s a mainstay on my A-Groove team. Anti-air Custom has already been mentioned, but one thing about the Ground Custom: if you do Towards + Forward into Standing Fierces, it’ll whiff against Crouching Opponents. ALWAYS start off the Custom with Crouch Short into Fireball + Short into Towards + Forward into Fierces. The knee will make Crouching enemies stand-up upon contact, so this will be guaranteed.
Learn the timing of his Towards + Forward Kick. Do NOT use it as offense, use it as a reaction. If enemy tries to attack but whiffs, throw it out, for example. Use it only as offense when you know the opponent is scared and not sticking moves out. Then, after the enemy blocks it, follow-up with Crouching Short into QCF + Short. Both characters recover mostly at the same time, though Benimaru may recover just 1 frame earlier. Because if you learn this timing, MOST opponents will fall for it and get nailed by the two-hit Combo. And if they start Blocking, do a Crouch Short, then ANOTHER Towards + Forward Kick. They’ll be expected the two-hit Combo, but you do that instead for pressure. An alternate follow-up is to Jump straight up and do Down + Roundhouse. Just for mix-up’s sake.
But put two and two together! After Towards + Forward kick, if your enemy just HAS to try to attack you afterwards, activate CC and do the BNB Custom Combo (end the Stand Fierce barrage with Towards + Forward into the Elec-Trigger. Just be careful NOT to mash Fierce too fast, or you’ll push Benimaru too far away. Do it with a rhythm).
Anti-air is a Jumping Fierce if you can predict their Jump. It’s really fast and can sometimes be used as reaction. Jump towards them with Fierce and when you land, grab them with a Benimaru Collider or Elec-Trigger. And if they catch on, just greet them with Crouching Shorts when they land and do Crouching Short x 3 into Fireball + Short. At this distance, though, you can’t tack on the D, U + Kick.
I don’t really play Benimaru much outside of A-Groove. I think, without a doubt, it’s his best Groove because his Customs are really good… 300% better than his Supers, IMO. Anti-Air Custom is really good, too. And he still has his Level 1’s for the Elec-Trigger, which is good enough (can’t jump out of it on reaction like you can against Level 1’s from Maki and Yamazaki). Running and Low Jump don’t bring much to the table for Benimaru, since he isn’t that good at Rushdown and his Low Jump is still higher than most people’s normal jumps.