@Alex-dono-sama
If i remember correctly, only the demon king can be rank 10 (though this depends on version, think grandpa was rank 10 in the anime but rank 9 in the manga) so in all likelihood iruma will reach rank 6 eventually, but past that it will be a much bigger hurdle.
@CKN by making him work, give them the money and party somewhere else without him. Or going to the casino while selling him off to cover the debt. Definitely not missing those creeps.