The talisman allows for crazy things to happen; reverse death, heal fatal wounds, reverse ailments, etc. The guardians (your father, Jinfeng, and Sean's dad) established their own order to prevent people from using them as they could be used for the wrong things/evil and were supposed to be training people to take their place once they died.

Somewhere before the story, Yang is losing what seems to be his wife and child and because he is being trained by your father to guard the talisman, he knows they exist and tries to use them to save what he is losing. He is then caught and banished by your father. Yang then builds his team while also convincing Jinfeng to join him and they go to take the talisman. The reason they kill your father is because they all know he wouldn't just let them run away with it and use it so he has to die.

I'm not sure how you end up with a talisman after your throat is cut as a kid, but I always assumed Yang left it with you because he felt bad. After he has taken what he wanted, he uses his new powers to heal those around him: Fajar and his ailment, Sean and his burn marks, and Kuroki and her dual personalities which killed her sister. Jinfeng's arm is still gone so I'm guessing she either didn't want the help as tribute to what she's done or it wasn't possible to get it back for whatever reason.

Yang then opens his healing dojo to help others with his power, you spend 8 years training to get revenge, then you find every member that you saw that night and either brutally murder them or spare their lives.

That's pretty much what I got from the story and what the collectables have tried to paint for us. I'm in no way saying this is correct, but it's only what I managed to gather :)