The stories are passed from child to child, whispered in the streets and on the playground like any good legend. “Don't ever venture beyond the wall and sight of the Tower,” parents warn, citing these cautionary tales that speak of the boy's many deaths. Exposure. Hunger. Sickness. Cutthroats. Living nightmares. And on. And on. The children, however, have their own truths. To them, the boy never died. They call him the Rat King. The children believe he leads the forgotten among them out of the City on grand adventures. They say he and his misfit army saved the world. But children say many things, and the Vanguard maintains their official stance: there is no Rat King and his army never existed. That's what the elders believe. I choose to believe otherwise.
The Rat King is an Exotic Side Arm that can be obtained via the following method.
1. Complete the main story of Destiny 2.
2. Travel to Titan and complete the quest "Enemy of My Enemy". Once you complete it, you'll receive an item called the "Rat King's Crew" in one of your Kinetic Weapon slots. In order to continue the questline, you'll need to perform the remaining steps with another player who also has the "Rat Kings Crew" item.
3. Together with your partner, complete three Patrol Missions.
4. With your partner, Complete two Public Events. They do not need to be Heroic Difficulty.
5. Play two or three Crucible matches with your partner.
6. Complete the nightfall with five minutes left on the clock. This can be tricky. Get familiar with the strike first and then form a fireteam with other players at this stage of the questline. After completing the quest, you'll receive the Rat King.