JKSManga
The beginning of the novel hints that the Witch in the human group might have been responsible for his reincarnation (it didn't, really, but you get the drift). My guess would be that she killed him and purposefully reincarnated him as a human due to knowing the coming of the Shadow Beasts, the system is there both to help him grow and shackle him from getting his power before he decides to save humanity. This would mean that the requirements for unlocking skills (saving humans) is not as farfetched as it may initially sound. The MC was being controlled like a cursed puppet all along! Author, add another reason for the extinction of the human race!