Originally Posted by vol 2
For example, when he fought Kayneth just then, Kiritsugu "sped up" his blood flow, haemoglobin metabolism, and muscle movement all at the same time. All that’s left is to use his quick reaction time to dodge the attack after he easily predicted the track the mercury whips would take. Kiritsugu is capable of accomplishing physical feats impossible for ordinary humans after he accelerated the time inside his body.
The biggest problem for this magecraft is the huge burden on the body.
The craft of time modification inevitably creates errors between the time within and without the bounded field. This error would immediately be corrected by natural forces when the bounded field is removed. That is, the "world’s own adjustment". Of course, this adjustment can only happen where "errors have occurred", which means inside Kiritsugu’s bounded field – his physical body. Adjustments have occurred in his flesh to get back in sync with the normal time flow.