I agree with Aazealh and Scott Rugeles in that I think it's not going to happen,. Though it was introduced as a weapon technique against the God Hand, the beherit-sword's purpose was ultimately subverted by Femto. So in my opinion, that card has been played.
However, many have toyed with the idea over the years, and there's one that I like hypothetically: In a final act of self-sacrifice, SK could urge Guts to plunge the DS through him, giving Guts' sword the same properties as the beherit-sword, but killing SK in the process. And while that
could work ... it still doesn't feel quite right, to me.
In the end, I don't think the crucial turning point will be a surprise weapon technique. I feel like Casca and the boy have an important role to play in bringing down Femto.
Similarly, there are endless theories about WHO WILL USE GUTS' BEHERIT online. But similarly, I really don't think it's going to be a conventional usage. What would be the point? Miura will have had something special in mind for this beherit, which has been with him since the beginning, and it won't just be another sacrifice.
Please forgive me if my idea below is stupid.
This continuation is going nowhere, so it might be the best time to post it.
So...
It might be weird but I don't even think that killing Griffith would seal the deal.
It would lessen the influence of the God Hand a lot, by killing the only member which has a physical body.
On the other hand, all of the people at Falconia would be at the mercy of the apostles.
And the remaining members would still be alive.
I think Miura would have played with the idea of the behelit behind used to take the Dragon Path and go to the Abyss, where Guts, Skully and other characters could inflict direct damage into the God Hand members.
Guts did talk something about "hitting 'em where it hurts" when he was at Flora's house.
Also, I think the idea to kill Griffith would involve attacking him when he is most vulnerable.
That is...when there's a fullmon and he's transformed into Moonlight Boy.
Yes, that would be very gruesome and it would be very painful for Guts and Casca.
And yet, I think it's the only way to directly kill him.
It would be their ultimate sacrifice in order to restore some amount of "peace".
Though it might not be the best idea.
We don't know for sure if killing the Moonlight Boy would kill Griffith.
And we don't know if the Boy is that vulnerable as well.
I think Miura would have explained something about this.
Partially related, another idea I've seen online (I don't remember where) and that could the stretch the story a lot, is that before attacking Griffith, they would force him to reveal his true colors to the people of Falconia.
Him appearing as Femto and getting his past being exposed, along with the knowledge that Pandemonium exists just behind the city (I don't think most people from the city know about it), could cause a heavy conflict in Falconia.
This wouldn't make the task of killing a God Hand directly that much easier.
However, he would lose the faith of the people he tricked to build his kingdom.
If he starts to lose his kingdom, he is forced to act in a way to regain this faith.
And it is in this very act that he may do something imprudent, something that makes him more vulnerable and susceptible to fail.
It hurts though because for me all of this doesn't really matter anymore.
I miss Miura so much man.
