>>678229>>678239I have two ideas of how to start this hypothetical adventure.
In the first one you are just a normal adventurer dude that comes across weird magical tome that have abilities of a Ero-Doujin Protag. Things like time stop, hypnosis, body modification and so forth. You obviously wouldn't be allowed to learn and use all of it from the start, having to chose one or two and working your way towards the others.
In the second idea you are a small imp / goblin like monster. You would either already have a ability to absorb others magical powers to grow stronger or also acquire it in some way early on the adventure, but you start very weak and need stealth / traps to prey on weak adventurers for some time until you build yourself up into an actual powerful Demon Lord.
Of course, in both you would get yourself a ever expanding harem of females to use in combat.