This is a vile, vile combination of hard hits that evil Ryu
are able to perform in some of the later incarnations of the Street Fighter
Guy from Final Fight has a move that is sort of similar, but it doesn't seem to do quite as much damage.
The synopsis of these techniques is that the screen goes black, and a few flashes appear while you hear a lot of thwacking in the backround. The screen lights back up to a picture of the character who'd administered the ass-beating, posing, and usually a knock out screen.
Ryu and Akuma perform this move by sliding towards the opponent. Shin Akuma slides much farther and faster (and he's a cheap bitch character). With the first two characters, timing is critical when you use this move.
Use a cross up jump kick if you can, and tap the buttons "Light punch, Light punch, Towards, Light kick, Strong punch", as you're coming to the ground, and then hit the final "Strong punch", as you touch, thus crossing them up into the combo, alternately, you can do it just as they're getting up, or when they're dizzy (Warning: This pisses people off).
The defense? Anything. Jump over, or just up in the air, or hit 'em as they're coming towards you. Jabs or light kicks are good, as you don't have to time them to get 'em in, and you'll usually surprise the opponent ("Hey, how'd you stop it?" imbecile) enough to follow up with a cute attack of your own.
Go. Fight. Win.