To get this, you need to have your opponent down to their lingerie, and then perform your Ultimate Shinobi Attack on them (Costs 5 scrolls; performed when your health is red).
The Ultimate Shinobi attack is unlocked by complete the respective mission for each girl in Chapter 4 of their school's Story Mode.
To make this easier, you'll want to pick a mission in Chapter 4 or 5, and pick Hard so they wont die as easily. You can use whoever you want, but I used Asuka.