Phantom Dust

First you need 10,000 credits to buy a 1-School Arsenal Case and most likely 50 credits for a Ki skill. You can earn this easily by playing the SP game normally or repeating missions on the Memory Box Terminal in the Visions HQ room at the start of the game.

Buy the Arsenal Case,

Multiplayer Mode>Xbox Live>Shop>Buy Arsenal Case. Then buy the case for 10,000 credits.

Setting up case,

Multiplayer Mode>Xbox Live>Lab>Edit Arsenal. Select the one skill case (Limit[1]). Open it and it will be full of Aura Particles. Select an Aura Particle and replace it with a Ki skill. Ki Skills are the skills with a Yin-Yang symbol. I had to buy one, you most likely will have to as well, info below.
If you are playing a real match you'll need to build proper arsenal, not just add one skill for boosting purposes.

If you need to buy a Ki skill,

Multiplayer Mode>Xbox Live>Shop>Buy Skill. Attack tab, scroll to the bottom and you are looking for the Yin-Yang symbol. Buy Swift Kick for 50 credits (or any other Ki skill).

Complete list of skills here - http://phantomdusted.com/pd_skills.htm

To win the achievement you have to select the single-school Ki arsenal case when setting up either a Xbox Live match or a split screen match. The opponent can't just quit, you either have to beat him or he has to kill himself.