In episode 40 ('The Congress Dances') of That Time I Got Reincarnated as a Slime, it's speculated that Demon Lord Clayman wants to attack the Animal Kingdom of Eurazania to awaken as a true Demon Lord. When the battle unfolds, it's not Demon Lord Clayman who is conducting the assault but rather an army of 30,000.
In episode 33 ('Putting Everything on the Line'), Rimuru says "taking out the invading army myself is a necessary part of [becoming a Demon Lord]".
My question is... if Rimuru needed to kill 10,000 humans himself and capture their souls, then why doesn't Demon Lord Clayman need to kill 10,000 people himself? Why is it sufficient for his subordinates to do it?
Also, if that was Demon Lord Clayman's goal, then couldn't he have killed 10,000 of his own men to awaken as a true Demon Lord? Or maybe he could have taken the souls of his men when they died, even if he hadn't planned on them dying?