For the game of Sharpen your sword each player will play with their own deck. For players new to the game, we recommend each player begins with a pre-structured strategy deck like the Stagnetic Deck or the Dryalight Deck. You can customize your decks from there- swapping out cards with others you trade with friends or collect in booster packs.
For the game mode "Hide it in Your Heart" or SOLO MODE (currently on the stretch goal horizon), you only need a single deck to play. You are still welcome to customize or add on to your deck by incorporating or swapping in other cards you may find in booster packs or other Animo decks, but that is entirely up to you.