no i know what you are saying but any ways he is never coming back
I found where I wrote some of my explanation so I'm pasting it here:
Them: "I think that Ghirahim might be Majora before it was put into a mask..."
Me: "What? Ghirahim being Majora? I don't think that it's possible: Majora is a part in female anatomy, also Majora's Wrath takes a female form.
The Fierce Deity Mask just seems too out of place in the story. The description reads: "Could this mask's dark powers be as bad as Majora?"
Ghirahim waited for the reincarnation of Demise to show himself: he knew that Ganondorf would be defeated. So what he did is he split himself along all three timelines in order to gather more and more power, then merge into an entity stronger that Demise or the Triforce when the timelines merged.
He followed Link into a portal that led to Termina, a place where the ancients of Hyrule sealed away their rivals from the war described in the Shadow Temple and the Forest Temple. They sealed it because they could not handle the power of the Kingdom of Ikana and Majora, and as soon as one of those two threats was eliminated then the seal would be broken.
Upon going through the portal, Ghirahim was sent back into the time of Majora and Ikana's war with Hyrule, the Stone Tower's war with the "gods," and Majora. Just like Majora, Ghirahim didn't die but was instead sealed withing a mask. Majora, who was more active than the Fierce Deity mask, kept it. The seal still held because there were two vast evils within Termina. Majora could not destroy Ghirahim nor could the Fierce Deity Ghirahim destroy Majora, because they were equal in might. Ghirahim was waiting for Link, Majora did not wait for anything.
By the time Link came to destroy Majora: Majora knew that Link could defeat her. So she gave him the Mask, hoping that Ghirahim would strike against Link and be defeated, and the seal broken. But instead Ghirahim lended Link his power, defeating Majora, and giving Ghirahim years to corrupt the mind of the Hero of Time.
Link struggled with Ghirahim for years, it killed his body, but Ghirahim preserved it for himself. That is why whenever Link came across the Hero's Shade it would attack him. Ghirahim was trying to scare the hero off, so he wouldn't learn from the Hero of Time's experiences. He was trying to bring the Shade ever closer to Ganondorf, that's why he kept getting ever closer to Hyrule Castle. Who knows? Maybe he reached the Thief...
That's just part of my theory, I skipped over a part in the middle. My idea was that Ghirahim (before being sealed) actually instigated all of those wars by offering power to the inhabitants of Stone Tower, land to the Kingdom of Ikana, all to destroy Majora.
Them: "There's one problem that i cant understand... if Ghriahim is controlling the hero's shade... wouldn't that mean that he killed Zelda? because Ghiriham's one goal woulda killed Zelda."
Me: "No. Because as many times as he would do that, she would just be back in a century. The problem is that Ganondorf is not Demise. He's the embodiment of Demise's hatred: all of Demise's consciousness was sealed away. That make Ganondorf the Imprisoned in "human" form. All he wants is to shroud the lands in darkness and to destroy them. Even Ghirahim doesn't want that. It's the same as if the Imprisoned escaped.
Ghirahim is ALLOWING (if not helping) Link and Zelda to defeat Ganondorf. Because each time he breaks free of the seal, he takes a little more of Demise's power from the Master Sword. There is eventually going to be a time where Demise is resurrected. Although by that time the timelines will have merged and Ghirahim will be more powerful than Demise.
Then Ghirahim will take Demise's power."
...(trivial conversation)...
Them: Why doesn't Ghirahim fight one of the Links or Ganon?
Me: "Because he knows that he'd lose. He's gathering power across the Timelines for when they converge. They will converge when Ganondorf has cycled through resurrections enough to siphon out enough of Demise's consciousness for Ganondorf to be more than just his hatred. Ganondorf will converge the timelines in order to make sure that he doesn't kill Zelda or Link only to have them come from a differing Timeline themselves. What he doesn't know is that by closing them he is reuniting three Ghirahims that each are possibly more mighty than Majora's Mask: to fuse and become something that overpowers the Triforce.
If that happens in the games then Ghirahim will be free to take all of the pieces of the Triforce.
You see that Ghirahim cannot merge the Timelines on his own, so he's counting on Ganondorf to break seals that sages or the Triforce has held him in. The seals are not weak, they were designed with Ganondorf in mind, so that he could never break out. But they were never designed with the idea of someone breaking IN.
Three timelines, three Ganondorfs, three chances that one of them will merge the times. Three Ghirahims breaking the seal in order for him to leach out Demise's intellect, or secretly help Link and Zelda defeat him when he doesn't.
I hope you or anyone else who like theories enjoys this!
Every character looks fun to play, can't wait to try out Ghirahim as well! 
