Demise

"Extraordinary. You stand as a paragon of your kind, human. You fight like no human or demon I have ever known. Though this is not the end. My hate... never perishes. It is born anew in a cycle with no end! I will rise again. Those like you... Those who share the blood of the goddess and the spirit of the hero... They are eternally bound to this curse. An incarnation of my hatred shall ever follow your kind, dooming them to wander a blood-soaked sea of darkness for all time!"

- The curse of Demise

Demise is the main antagonist and final boss of the Skyward Sword. Long ago he and his horde of demons and creatures broke through a fissure in the earth and sought out the Triforce. However, he was defeated and sealed away by the goddess Hylia.

Throughout the events of the game, Demise attempts to break free of his seal in the form of The Imprisoned, but he is consistently repelled through the efforts of Link and Groose. At last, when Link obtains the Triforce, he manages to defeat Demise permanently. However, Ghirahim kidnaps Zelda and takes her to the past through the Gate of Time, where he begins a ritual to revive his master. While Link manages to defeat Ghirahim, he is too late to stop the resurrection of Demise. The Imprisoned begins to absorb Zelda's soul and eventually transforms into the Demon Lord himself Demise. Ghirahim welcomes back his master but Demise pulls the Dark Master Sword out of Ghirahim and absorb's his entity into the sword. Demise begins to absorb the soul of Zelda to gain unstoppable power which Groose notes he still hasn't obtained, but he is impressed by Link's willpower to protecting the goddess for a human who would normally flee at sight from him and invites him to do battle. To Demise's shock, Link manages to defeat him, but in his dying throes, he places a curse on Link and Zelda. For all eternity, they and their descendants shall be pursued by a manifestation of Demise's hatred. With that, Demise is sealed away within the Master Sword, where his remains begin to decay.

Battle
After Link enters the chosen battlefield through the portal in the past, Demise will praise him for his courage, but then will tell him that when he falls, he shall rule over everything in the world. With that, the battle begins. Striking Demise through his guard can be difficult and he will often retaliate immediately. Link's Skyward Strike is unavailable as the power of the Goddess is negated by Demise's personal battlefield. Link can quickly Shield Attack when Demise attacks with the Ghirahim-sword, then follow up with a vertical attack or Spin Attack. Eventually, Demise will be thrown backwards, seemingly defeated, but he will rise up and summon a storm. Demise can then draw the lightning from the storm to charge his sword with electricity. Link will now be damaged if he strikes the sword and Demise will cause twice as much damage as before. To defeat Demise, Link must chose his attacks wisely. Demise is now able to perform his own variation on a Skyward Strike, after which he is forced to recharge his sword by pointing it skyward. It is possible to defeat Demise by attacking him before he can recharge his blade, but it is easier to mimic Demise and point the Master Sword to the sky. This will charge the Master Sword with electricity, allowing Link to attack with a Skyward Strike and paralyze Demise, making him vulnerable to attack. After doing this a few times, he will fall back again, allowing Link to finish him with a lightning charged Fatal Blow. Demise is swift however, and will likely dodge the attack at first. If Link is quick enough to land the attack, the battle ends.

Trivia

 * The sword he holds is a dark version of the Master Sword. It was pulled from Ghirahim's chest, and appears to contain the remains of his soul. At the end of the battle, it fades away to nothing before Demise begins to crumble.
 * His fighting style is similar to Ghirahim's, except his is much finer.
 * Demise will stare at the Bug Net if it is brought out, similar to Ganondorf staring at the Fishing Rod in Twilight Princess.
 * Demise has a strong resemblance to some Ganondorf incarnations in other games.