Thread:Stray Bird/@comment-28048698-20170613021249/@comment-28209103-20170725141740

It's not about capability of the body, attaching servant arms to non-servant is not matter of physical transplant but more on mending the souls rather than physically attach an Arms or donating a heart to a body. There's few plotpoint that they glossed over :

1.Transplanting servant organ is an act of fusing 2 spiritual body not physical, lt is normally impossible unless the recepient is compatible with the donater. In Sieg case they kinda explain it that Sieg is extremely pure... uhh,, yep that's all.. so can we take it that he got no such thing as personality? no wonder he's called the worst fate MC ever by some.

2. Transplantion requires a spiritual doctor, not some magical light that magically transplant the organ by magic..

3. Once attached physically it's said to be impossible due to the servant part overwhelmingly more powerful than any mortal. In Shirou case his body cannot wisthand the pressure that his body can be literally blown away by just the power left in a single arm of EMIYA class servant (which is pretty low) thus he need to seal it. Meanwhile Sieg have no real negative reppercusion from taking Siegfried heart,, which is said to be close to heart of dragon I believe? So a hommunculus which is all magic circuit and no real body strength nor mental fortitude conveniently become stronger rather than exploding from the dragonic power? legit. where's the whole servant power invading the body part? where's the excruciating pain from being invaded by foreign being? oh right conveniently becomes command seal to morph into Ultraman for 3 minutes.. wow Shirou must be jelly.

4, Siegfried heart does nothing to Sieg mentally, physically aside, mentally the heroic spirit Siegfried should've corroded his mind over times distort his judgement, and give flood of information while invading his whole body, Compared to few days old hommunculus the spirit of a servant must be infintely stronger as such he should've been swallowed by it faster, especially since he didn't really take any measure to seal it. Meanwhile due to his spirit being weaker than EMIYA eventually Shirou will die, even without using the power in like 10 years, if he trained (yes, trained, not getting buffed by magical heart transplant) he can at least seal it(yes, seal not use) without the shroud.

To be fair I am aware that Archer arm affected Shirou body somewhat, however Shirou base body is already pretty good in the first place and the buff comes with the risk of dying anytime and pain that enough to drive you suicidal. Sieg need to give Shirou some sumanai for how easy his life is..