You can't take any damage at all with this, even if you use the QR code that stops your health going down, Taking damage will still count. However there are a few good strategies for this one. Either way your going to want to fight Raditz (Score Attack > Saiyan Saga > Raditz) and obviously set the difficulty to Hard.
Bardock 20x Kaioken Method:
For this one your going to want to scan in the QR code for Bardock Super Saiyan (although any character with A-rank attack will work), then scan in the code for 20x Kaioken. From here begin the battle and immediately dodge left. This is where things become more luck based, but your looking to charge your Ki Meter up enough that you can jump (indicated when the box appears above the Ki Meter). Basically you want to hope that Raditz will block, which will give you the time to charge it enough. I had the most success when the battle started in the air. Once you are in the quick-time event where you must melee enough to fill the bar (hopefully succeed otherwise you'll need to restart) you should be far enough away that you have time to charge your bar halfway and use Bardock's first Super Attack, if you do manage it will 1 hit kill Raditz!
Kid Buu Unleash Ki Method:
For this you want to read in both the QR codes for Kid Buu and for Unleash Ki. The reason for choosing Kid Buu is that Bardock's Super Attack often seems to be hard as hell to pull off as they require odd arm and leg placement and Kinect doesn't want to play ball most of the time. Another reason is that Kid Buu's second Super Attack is easy to pull off quickly, but you can choose anyone you want for this method really, although someone with A-rank attack would be preferred, if you don't want to use Kid Buu. What you want to do is as soon as the fight starts, dodge left and then raise your hand up (or the appropriate gesture for your second Super Attack). Dodging left should give you enough time to pull off your Super Attack. As soon as one Super Attack is done you'll be at Ki Blast range and should be golden. Just keep spamming Super Attack's and you should be done soon enough.
Notes: On Hard you'll likely find the enemy countering your Super with their own. It's much harder to fill the Assault Gauge on this difficulty so be aware and try to start punching when you see the the camera move to Raditz the second time so that it starts filling up a little bit sooner rather than waiting for the Gauge to appear. Another thing to note is that to do more damage with your Super Attacks you need to hit it when the icon lights up with the square around it. Finally you can't win with a normal attack on Hard (e.g. using a Ki Blast when the enemy has 100 health) as it will only go down to a minimum of 1.