For this class, you must obtain 300 Dragon Shinobi Tokens and trade them in at /shadowfortress (or /blackfridaywar if you want the Shadow variant in November). You have two options for this:
"The 8 Heads of Orochi"
If it's not Black Friday (November), accept this quest from Ai no Miko at /shadowfortress then defeat the 2nd and 3rd Heads of Orochi (or any screen with two). Make sure to have completed the storyline from the Requirements section first.
"Dragon Shinobi Tokens"
If it is Black Friday (November), you will have access to this seasonal quest from Twilly at /blackfridaywar. If you're in a group, farm BOGOdrone Prime and Executive Assistant Vordred. Otherwise, just farm a room with a Deal Bot 2.0 and Hypnotised Shopper. This quest is overall easier to complete.
DragonSoul Shinobi and Shadow Dragon Shinobi are duplicates of the Rare "Dragon Shinobi" class. If you are an older player who owns that, you do not need this class.