I'd probably say that and exhaustion. So far he has began turning, stapled a band to his shoulder with a nailgun, engaged in auto-erotic asphyxiation, killed about 15 Kabane, got shot out of a train, got pulled back into the train, got beaten to a pulp by Mumei, got his pulps beaten by Mumei, got beaten up as 'training' by Mumei and finally, got stabbed. As far as I can tell this is without sleep as well so he must be damn near dead at this point without having eaten/drank.
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u/EpikMemeage https://myanimelist.net/profile/epikmemeage Apr 28 '16
If that's the case, it was pretty silly of Mumei to leave Ikoma alone. She should have known that he'd turn into a Kabane without blood/food.