The Divine Dragon is the final boss from the Fountainhead Palace area. To reach this area you must stay loyal to Kuro thus this boss is tied to the Immortal Severance ending path. This boss differs from the rest as the encounter involves unique mechanics, thus there won't be any recommended items. This fight divides in 2 phases, during the first one you do not fight the Divine Dragon still, but the Old Dragons of the Tree.

Phase 1 - Old Dragons of the Tree

This encounter is very easy, it consists on killing all the tree looking dragons that will keep emerging. You will damage the health bar above for each one you kill; be careful as they cough poison though. Once you have killed a few, be aware of the trees emerging from the ground. You can actually grapple onto them and then perform an aerial deathblow over the old dragons. This will make a special animation in which you sweep your blade all over the area killing all the old dragons that may be around, which will deal massive damage to the health bar and end this encounter quite fast.

Phase 2 - Divine Dragon

After the previous phase, you will fight the Divine Dragon. He has two attacks, one is a sweep wave that you can avoid by jumping and the other one is an overhead frontal attack that can be easily blocked or dodged to the side. You can also keep grappling onto the trees here to avoid his attacks.

In order to damage him, you must grapple into the one of the trees that will be charged with electricity (it will be sparkling). You will immediately elevate to the sky and you must then press the attack button to throw a lightning bolt towards the dragon (make sure to lock onto him while doing this to not miss) dealing damage to his health and posture bar. After his posture is broke, the trees will immerse back to the ground so you won't be able to use them. During this period you must survive the dragon's attacks. After enough time has passed, three trees will emerge this time, one of them will be charged, grapple onto it and you will elevate twice in the sky for a final lightning bolt. After that the Dragon will lay on the ground, approach his head to perform the deathblow.

Check the video below if you need visual reference.

Divine Dragon Boss - No Damage

Credit to THE GAMER EYES for the video.