You get this by equipping a school and completing matches in pvp. Go to an altar, select combat trials. Before you press anything, on the left of the screen you will see your school and a button at the bottom saying equip all. Use the deck in pvp, you will see a blue bar come up after the match ends. When you level up, back out and keep equipping them as the more you have equipped, the faster you level. Once you get to level 7 with the school, it should pop automatically.