How do you kill the Divine Dragon boss in Sekiro: Shadows Die Twice? This boss fight found at the end of the Fountainhead Palace area is intimidating, but is actually relatively straightforward. The unusual patterns may throw you, but it shouldn't take you too many goes to defeat this gigantic creature.
Sekiro: Shadows Die Twice - How to kill the Divine Dragon
There are two phases to this fight. The first is pretty simple -- attack and kill all the white dragon enemies. They go down easily, but there are lots of them, and every so often they summon trees from the ground that can damage you. Grapple up and attack an enemy from above. This will trigger an area of effect move which will get rid of surrounding enemies. You need to repeat this until all the enemies are down.
The second part of the fight is when it ramps up and you fight the Divine Dragon proper. The aim here is to grapple up to the trees. Every now and then, one of them will be struck by lightning. Grapple to that tree so that you can attack the dragon with a lightning deflect. You need to keep doing this until its posture bar is full. In the meantime, you'll have to deal with a big vertical strike and a horizontal sweep; dodge or block the former and jump over the latter. Once its posture is broken, it will start thrashing about and the trees will disappear. You need to survive the onslaught of attacks until the trees appear once again, when you'll be able to do one last lightning attack. After this, go up to the Divine Dragon to deliver the final blow.
Killing the Divine Dragon gives you the Divine Dragon Memory, Divine Dragon's Tears key item, and 12,000 XP.