The Elder and Groose are there. The Gate of Time opens and the seal placed by Zelda is shattered. Zelda wakes up and falls into your arms. You then go back to the Elder and a quite emotional Groose ^^, then Ghirahim appears! He wants to bring Zelda back to the past to bring Demise back to life again! Even though Groose and the Elder are trying to stop him, as Link is powerless, Ghirahim goes back to the past taking your friend along. Talk to the Elder, then open the Gate of Time.
FYI: To go on your quest, buying the Sacred Shield is strongly recommended (and even upgrading it to the "ultimate" stage), as well as a protection potion and a healing potion.
In the Temple of Hylia, talk to a hurt Impa who will inform you that Ghirahim went out from the front doors. Get those double doors opened.
Ghirahim is at the bottom of the pit, performing a little dance and lifting Zelda to execute a ritual that would bring Demise back to life. Then he will make tens of Bokoblins appear while the sky is darkening... Fight the red Bokoblins while going down the pit. When some yellow barriers block your way, you have to get rid of all the remaining enemies to get past it. There will be three Moblins with wooden shields, and further some Archer Bokoblins and bomb carriers that are easier to avoid along with an army of Red Bokoblins. Upon reaching the bottom of the pit, Ghirahim will protect himself and send around twenty Bokoblins at you. Get rid of all of them, and the demon tells you that you're too late. Apparently really bothered, he doesn't want to be disturbed during his ritual! But in his rage, he throws Zelda in the air to take care of you. Then the ground under his feet tears apart and rises while taking you as well. Getting angrier and angrier, he will take off his cape and white clothing. He pretends to have been very kind with you and have endured it all with dignity! Indeed! Now black with white eyes, he wants to make you suffer the ultimate torment: the Endless Plunge.
Ghirahim, Evil Lord
Use the Z lock during the whole fight and hit him with your sword, even though it seems to have no use. Indeed, it only makes him draw back and fall from the arena. When he falls, jump towards him and give him an Ending Blow, even though he stands up again. Keep on fighting him to make him draw back while still being careful to his punches and kicks. Sometimes a cursed magic will spring from his hands. Quickly swing your sword to the other side (if his hands are vertically positioned, make a horizontal swing, and vice versa) to keep him drawing back. After two more Ending Blows, the arena will lower and the second phase will begin.
After a close shot at his chest, he now wields a huge blade to attack you. Raise your shield when he is ramming at you to hit the diamond on his chest with a thrusting strike. When he temporarily loses his blade, take advantage of this to slash him in the chest. Keep an eye at your shield gauge and don't hesitate to get away for a moment until your gauge refills. If he throws small daggers at you, protect yourself with your shield. If he throws energy balls at you, reflect them back at him with your sword in the same orientation as the spheres (horizontal or vertical); after three successful reflections, he is disoriented for a few seconds, so rush at him and give two to three thrusting blows. After hitting him between five and seven times, he will lose his sword and get a bigger one!
Try to avoid his hits as much as you can, raise your shield when he is ramming at you and he will protect himself with his blade. At this moment, you have to hit his sword relentlessly to break it. If the sword is held vertically, do horizontal strikes and vice versa. You will need less hits if you manage to attack his sword from the two halves of the blade by hitting it from right to left and from left to right (or from top to bottom or bottom to top). As soon as his sword is destroyed, strike him as much as possible to badly hurt him, but if you can't get to break his sword in one go, it will regenerate. Break the sword three to four times before hitting him relentlessly to defeat him once and for all!
Shocked that he got defeated, he informs you to that the ritual was completed during the fight and that his master will absorb the Goddess's soul to come back to life. The Imprisoned will appear and absorb Zelda's soul! Ghirahim laughs at his victory! The monster takes a more "human" form with fiery hair. Ghirahim bows down at his master, but Demise makes him float and takes a long blade from his body. (Could Ghirahim be Demise's blade, like Fi is the Master Sword's spirit?) As Demise throws Zelda in the air, Groose manages to dive and catch her. After the Demon offers you another place to fight, Groose cheers for you since the Elder said it's still possible to stop the fusion between Demise and the Goddess. Demise disappears while trying to discourage you once again.
It is now time to refill your hearts, find some Pieces of Heart, buy some more potions and buy/improve your shield. Then, once you feel ready, come back to this place and step into the purple rosette to begin the fight.
In a strange landscape between water and sky, you find Demise ready to get rid of you to possess the Triforce and take over the world. To begin with, you just have, like in the fight against Ghirahim, to raise your shield when he is charging at you and quickly hit him with your sword. Do this around twenty times to make him angry and you will see him casting lighting into his sword and body.
In the second phase, he will raise his sword skyward, but you can do it too! Prepare your sword for a Skyward Strike and directly aim at him since he is also ready to attack you. If you succeeded to reach him, dash to him and strike him as much as you can with your sword! He will fall down... Never get too far away, because he will take advantage to dash at you which will be really hard to avoid and hurt you badly. Repeat this attack twice more, then on the third time, when he falls down, it's time you give him an Ending... Blow!
But before vanishing, Demise says that this isn't the end, that this story will repeat itself and he curses both the Goddess's heirs and Skyloft's inhabitants. However, Demise got destroyed, what's left of its soul got absorbed by the Master Sword and the seal got closed again. Once back on Hylia Domain, Impa congratulates you. Zelda is happy that all of this is over, while Groose is boasting... but only to make you laugh. Fi also appears and says that you are the hero that vanquished Demise and protected the Goddess. Therefore you don't need her help anymore and she's asking you to release her by putting back the Master Sword into the pedestal. Once you did so, she adds that her mission turned into a precious memory, a happy moment... Impa, for her part, says that she belongs to the past and that since Demise got sealed inside the sword, she has to look after it. As a member of the Sheikah tribe, she is proud of being chosen to do this task, but Zelda is sad that she has to leave her after all this time together. She gives her one of her bracelets as a memento...
Its power is too great to leave in the grasp of man.
Dependence on its might is an invitation to disaster.
When it has served its purpose, it must be secreted away to lay dormant once again...
the knowledge of its existence hidden from mortal history.
Once back to your era, the Gate of Time will vanish. The Elder is there and is wearing the bracelet given by Zelda... and yes, it is Impa! who will also vanish, while the Master Sword is shining on its pedestal...
After the ending credits, in the Sealed Grounds, Gaepora will get his daughter back. Groose and his friends are flying on their Loftwings under Link's and Zelda's watch on the Goddess statue's hands. Your friend was longing to see the surface and wants to stay down there to feel the ground under her feet, raise her head towards the clouds and protect the Triforce... How about you?