it is revealed that naraku is a half demon because he still has onigumos human blood in him no matter how much demon blood he has. in episode 71. it is revealed that unlike inuyasha, naraku chooses his day of the month to be human. and there he strenghens the strong parts of him and throws away his weak parts. episode 71 is the first and probably the only time inuyasha fights naraku one on one instead of a demon puppet.
Submitted by the lord of the anime spoilers