Finally, the harvest festival approaches
@steeivevonbeevie orc lord wasn’t a true demon lord and never got 10k souls. Millim who slaughtered a whole kingdom is a true demon lord so rimuru is following the story. The revival will only be possible if he becomes a true demon lord.
Also, I never thought about the fact it had to be human souls before so interesting to bring that up. But if you just think about it a little, humans and monsters are distinct(monsters evolve and get power with names, humans don’t) so it probably has to be human souls. I don’t think it’ll be explained why it has to be human but as I said rimuru is going off of millims precedent and he just so happens to have a supply of human souls to work with.