The description is very vague, and possibly misleading. For this achievement you must charge your
Ki Meter from zero to max in one go, without taking damage, with Ki Charge. The best method seems to be the following: Go to Score Attack > Saiyan Saga > Saibamen (although Raditz will work equally as well). Set the difficulty to easy and begin the battle. From here do literally nothing except wait until the Saibamen activates the jumping Assault Gauge quick-time event when this happens take the Ki Charge stance. When the quick-time event is over you should be at Ki Blast range, and immediately begin charging your Ki Meter, if all goes well it should unlock.
Notes: The reason behind not attacking is that if you succeed in the quick-time events you will get a small amount of Ki, so just avoid doing anything. Also the timing on this is ridiculously close to failure, so if your not fast enough at beginning the Ki Charge, you will fail. To reset your Ki Meter either restart the fight or charge it to full and use your Super Attack but fail to hit with it. At this point your meter will reset to zero and you will be back to the Ki Blast distance.