Board Thread:General Discussion/@comment-26475399-20151228215405

So i'm aware that many people within as well as outside of this Wiki have considered that Ichigo having performed the Final Getsuga Tenshou was him unknowingly using the Quincy technique of Letzt Stil. I am currently a strong supporter of this theory. And here i'm going to go into some detail to explain how my theory applies to the whole situation. This will be long for a main post, so get comfy.

Okay, so let's refer to Chapter 409 to start off. This page, specifically.

Although he obviously knows of it, Isshin doesn't outright say that he himself has learned the FGT.

"These guys don't want to teach us this technique." In the case that Isshin doesn't actually know it himself, you could say he admits that he couldn't learn, although he tried.

"You'll soon see why." His following quote hints that he very well has actually learned it and knows of its aftereffect; but it's still not blatant enough to say he absolutely has learned it himself.

Let's keep our focus on that for a moment longer. Ichigo returned from FGT training with over-the-top powers and Reiatsu, and his Zanpakuto had fused with his arm. Isshin doesn't have any of those features to signify his own FGT. Although, you could say that maybe Isshin, being a more experienced Shinigami, (if he has indeed learned FGT himself) would know how to suppress the Reiatsu output as well as somehow cancel out the physical display. Or maybe it's just that his FGT isn't nearly as strong as Ichigo's and that's why he never wanted to use it, as it'd be in vain.

It wouldn't be a stretch to credit Isshin for being the first Shinigami to learn a unique technique, and be the first to ever learn such a technique that all Shinigami are technically able to attain, though unknown to them.

It's highly possible... but that's not the theory I'm getting at. ;)

Now let's go back in the timeline and refer to Chapter 241. At about the middle of this chapter is when we see the meeting of Isshin Kurosaki and Ryuken Ishida. We don't see their full conversation, but my theory involves what the unseen rest of their visit could have been about.

According to my theory, Isshin's goal was to get Ryuken to teach him all about Letzt Stil (something Isshin could have learned about from Masaki, or learned of elsewhere), and then Isshin would try to apply the basic principle to his own Zanpakuto, and attempt a Shinigami version of the same technique.

Isshin knows that Ichigo is half Quincy. He knows Ichigo's Zanpakuto is called Zangetsu, as well. He may or may not know the whole deal of Ichigo's true powers, but he at least knows that Ichigo is half Quincy. That in mind, he confronts Ryuken about Letzt Stil -- and if he as a pure Shinigami cannot perform it, then he has hope in the natural Quincy powers of his son.

(A quick note: Why would Ryuken teach them Letzt Stil rather than the better and much less costly alternative of Vollstandig? Ryuken Ishida is the son of Soken Ishida, who denied modern Quincy techniques, a category into which the Vollstandig method falls. So if Ryuken (who denied any desire to identify as a Quincy himself) ever learned much from his father, it would be Letzt Stil rather than Vollstandig.)

So there's that. Now let's look at Ichigo and his FGT training.

The main thing that convinces me of Ichigo's FGT being a Letzt Stil (whether or not Isshin has learned his own FGT), is one overlooked detail....

Jump ahead in the timeline and refer to Ichigo's Soul Palace training and true Zanpakuto forging. Old Man Zangetsu says that any time Ichigo needed Zanpakuto training, he would use the Hollow to do so. Therefore, any time when OMZ helped Ichigo by himself, it wasn't Ichigo's true power that was being strengthened, as OMZ had a hold on Ichigo's real Zanpakuto powers (i.e., Ichigo's Bankai training, which wasn't actually his true Bankai).

Now take that fact, and apply it to the FGT training. Who trained Ichigo and taught him the technique? It was Tensa Zangetsu. Yes, Tensa was merged with the Hollow, but Tensa was the dominant personality in this merged form. Old Man / Tensa Zangetsu was Ichigo's Quincy powers. The fact that the Quincy spirit was the one to train Ichigo, has me convinced that it was indeed a Letzt Stil performance.

So, here's the overview:
 * Isshin may or may not have learned a Shinigami version of the Letzt Stil himself
 * Ryuken could have easily been the one to help Isshin in learning the technique
 * Ichigo learned a Quincy-similar technique, from his inner Quincy spirit

An ending note, i believe Ichigo could easily bring back his Final Getsuga Tenshou form, but as a Vollstandig, so that he can use it indefinitely as well as return from it without any dire consequences. 