First weapons Achievement
Confirm your first self defense technique.
From the main menu select "Self Defense Rehearsal" then "Class 1. Wrist Grab". The very first one is called "Crossed Wrist Grab", and that's the one you need. This will only take about 5 minutes and only has 4 different motions. Complete the segment a few times to get the hang of it, then again during the "real life" situation. Once you complete all of the techniques the achievement will unlock.