Siegward of Catarina is a new NPC in Dark Souls III, and there are multiple steps to take in the game if you wish to see his story through to the end. You’ll first encounter Siegward in the tower with the giant at the Undead Settlement. Take the elevator up to talk to the giant, and when you’re on your way back down, hop off the ledge to find Siegward staring at a fire demon. Engage the fire demon and kill it with Siegward. Talk to him three times to get the Siegbrau, and two gestures.
After defeating the Deacons of the Deep, check the well outside the Cleansing Chapel to find Siegward trapped without his armor. You’ll have to get his armor from Patches to continue this quest. First, you have to buy the tower key from the Shrine Maid to access the tower behind Firelink Shrine. In the tower, take the elevator up to grab the Firekeeper Soul. On your way back down, you’ll notice that Patches has locked the gate behind you, and you’ll have to drop down the coffins to make your way out. You’ll find Patches at the top level of Firelink Shrine, and you’ll be able to buy the Catarina armor set from him. Return the armor to Siegward at the well and he’ll give you the Rejoice gesture.
After that, in Irithyll, you’ll find Siegward again in the kitchen past the sewers with all the spider ladies. He’ll be next to the fireplace and you can talk to him to get another Siegbrau and the Emit Force miracle.
Progress through the game normally until you find the Profaned Capital. Siegward will be trapped in a cell in the Irithyll Dungeon which can only be accessed by going through the Capital. First you’ll need the Old Cell Key, which can be grabbed in a mimic chest at the end of a long sewer tunnel where you face the tiny rats. After that, follow the path normally until you reach the Profaned Capital. Instead of taking the ladder that leads you to Yhorm’s area, look out for another ladder that takes you to a hallway with a crystal lizard. Follow the path until you reach a ledge overlooking a toxic swamp with the spider ladies.
Cross the swamp to get to a ladder taking you upwards to a hostile NPC on the roof. Look for a small window facing the blue roof – that’s where you want to jump to. Once you make the jump, follow the linear path to Siegward’s cell and free him. He’ll reward you with a Titanite Slab. He’ll now assist you in the fight against Yhorm.
After defeating Yhorm, Siegward will drop his armor set, his shield, and another Stormruler sword for you to pick up.
For more tips and tricks, be sure to check out our Dark Souls III wiki.