Thread:Stray Bird/@comment-28048698-20170613021249/@comment-28209103-20170725171131

because it's all about the spiritual body, and because Shirou is the sole successful example of transplant of foreign spiritual body to other spiritual body. the basic premise still stand no matter if you're hommunculus or human or between servant that fusing 2 spiritual body should be impossible for there'll be rejection.

Illya and Iri absorb the defeated servant soul into them not fusing with it, that's apple to orange comparison and apparently Sakura are better than those Einzbern Homunculi at absorbing stuff. Transplation of Heroic spirit organ still retain the property of that heroic spirit, meanwhile even Gilgamesh lose all semblance of personality once Sakura turned him into magical energy thus the two are not equal.

I've don't really need to repeat this but suppose I have to Siegfried technically is still alive, his spiritual body still exist partially as Sieg heart, however as per previous lore explanation this have 2 implication that form the premise of the organ transplant :

1. the process of transplanting a part of servant is operation of fusing of the soul. Even if it's miraculously succeded the stronger one shall devour the weaker one. Even EMIYA (which is weaker heroic spirit as you said not to mention "only" his arm) will devour Shirou, so why should the heart which is infinitely more stronger as power source from stronger heroic spirit doesn't devour Sieg? not even a little bit? nadah? nothing? oh right a sudden power tattoo to become Ultraman.

2. Heroic spirit organ even when it stabilized and materialized as the host still contain the power of the heroic spirit which is not something the body can handle, even a robust guy like Shirou will be blown away if he fully opened the seal and let the excess power flow. meanwhile somebody just feel all Okay with Siegfried source of power circulating within a body that can't even walk by itself. For Shirou even doing nothing will make his arm overheat for no reason and sent the excess heat to the body,, however I never heard any of such problem in Sieg, the heart feels like it's at home even tho a heart should be constantly active, even more than a 'mere arm'

The principle of Magic circuit usage generate heat is already set by Kerry, probably the magic circuit from Servant seems to generate way more heat than human can handle even if it's just residual power from 'mere arm' I wonder how hot a dragon heart can be?

Those two premise should apply to everything from Servant to human to Servant to servant because the basic fundamental description  is that the transplant is a method to attach spiritual body to another spiritual body, If the organ are not compatible it'll kill the recipient, even if it's succesful the since the organ are still alive the stronger spiritual body will devour the weaker one (which translate to kill it), it'll affect body but not drastically and it should retain power of the donor that have power too awesome to use which can

And of course the Nine lives Blade Works is more believeable because Herc already loses his God Hands and already rotted, the cost of the technique itself is not that high cuz it's essentially body reinforcement + Projection and the biggest risk is instead using the arm of Archer for the high speed movement which resulted in his whole body feels like hot as hell afterward from the excessive heat on Archer arms, if he's given for example Heart of Archer then I'm sure his arm will be broken before he could even swing Berserker Axe sword, because it is Archer arm that he's capable of using Archer full extend of power only in that arm. However his mortal body cannot take it thus it'll break down. Compare that to become full copy of Siegfried in a body that can't even stand at beginning,, oh right the heart conveniently buffed his body from something weaker than baby and he only feel the backlash if he used up all of his power as Siegfried,, riight

The transformation itself is a BS but that's spoiler so I'll get to it once it happen. What I hgihlight is not the change, Shirou change are negligible that only once he's in action it is shown that his body become slightly tougher but that's is one of the other side effect. what there is not is the reppercusion of fusing 2 foreign spiritual body. This is why I said lore in apo si clusterfuck and you better just turn your brain off and accept it as it is.