@Dirtbug
Assuming that these humans are the original humans I don't recall it being said that they were individually strong only that they were strong as a race. Their souls were also different from later humans and retained memories, perhaps this early in the universe they haven't accumulated...
So he can probably only use spells that use 10MP max, but he can use them infinitely... poor demon lord is going to die to chip damage.
As for HP, would he die if he took 11 points of damage or would it not change at all?