I have never been a subject demon, only ever a king. But as a king, it is an experience many people would thoroughly hate. Most kings don't attain immortality because of the process that you must go through. It wasn't much in the way of power I sought, but merely to be the best. To become an immortal demon king, you have to kill the people closest to you. I hated the thought, but I was left with no choice. It was either the entire planet, or only my two children and wife. I feel immense regret for that day, but they are always allowed into my kingdom, and no one dares touch them. Despite the down sides of it all, you gain great power and skills that only other gods, or deities could know. I know the weakness of the others, and they all know mine. So it's a weakness information trade, in case there is a reason to take them down in a sense.