Play games
Choose the game that interests you and play itfor free.
Complete the quests
Every game has some quests for which you will receive Soul Gems.
Receive rewards
You can exchange your Soul Gems for Steam Wallet top-ups, game keys, CS:GO Skins and other rewards.
Now, I don't watch the Anime and I'm deciding if I even should but this game is dope/cool, even if I'm not a One Piece fan I still find this interesting.
I may as well just watch the Anime someday in the future just because of this game.