You can earn this as early as "After School" on Monday the 18th of April.- Whilst in a dungeon, after getting a "shuffle" where you choose a reward after a battle, select "Skill card" as one of the options where possible.
- Then visit the velvet room. You can get the from "Shopping District, South" as early as 18/04. It's the blue mystical door.
- Select "Utilize Skill Cards", then select "Give Skill Cards" and "Register All".
This will register any skill cards you have and unlock the achievement.