I play Vega with a keyboard, and I agree that it can be blisteringly hard to master his ultra input. There was an old thread on this forum (“Vega on the PC!” I think) that helped me a lot, though, and there are some shortcuts that make it less than impossible without hours of practice.
That said, god help you if you’re trying to do Zangief’s ultra.
The first and easier of the two motions involves abusing the heck out of input shortcuts. Using the standard arrow key layout, hold a :db: charge using two fingers on the appropriate keys. Once you have your charge, use your third finger without lifting the other two from :db: to quickly tap :r:. In training mode, you should see that the game registers this as :df:, and then when you lift your finger quickly returns to :db:. Complete the motion by releasing the down arrow and (while still holding the back arrow) press up + KKK and you should see roses.
There are two big problems with this method, though; the biggest being that it’s slow. Because you’re relying on the game to correct itself, there’s a predetermined “max speed” of input for this, and with the extremely tight timing required to actually land this attack, the ease of execution is offset by reduced usefulness. Additionally, if you try to do the ultra too hastily using this method, you will wind up doing an EX barcelona to the back wall, which always makes me die a little inside. I might be deluding myself, but I find that the risk of an accidental EX barcelona is reduced by double-tapping the :df: input. It also feels faster, but I think that’s just in my head.
The other limitation is that this input method is incompatible with FADC to Ultra, which is extremely important for when your opponents stop spamming fireballs at you from max range or otherwise begging you to punish them with some bloody roses.
Edit: a variation of the above input method is harder to do, but can help to offset the speed limitation by making things more manual. Instead of holding down :db: for the entire sequence, instead hold down only the down arrow key while you input the :df: command. Think of it almost as if you’re swinging your hand from left to right to left again using the down arrow as a pivot point.
The second is, well, the standard ultra input: :hcb: :ub: :3k:. The important thing to learn this method is to recognize that all you need to do is hit three keys in proper sequence: forward, down, and back arrow keys (for the hard part, anyways). If you allow your fingers to roll across the keys like you’re strumming your fingers, the game should automatically plug in the diagonal directions you’re going for. Between the two, this method is by far the more worthy and useful at higher level play, and if you’re trying to find one to practice for implementation in your game, this is definitely the one to study.
Still, input method no. 1 should get your Bloody High Claw going in about ten minutes, tops.