You beat up the Leviathan the bad magician guy summons, and bring your evil brother's cheating to light for punishment by the kingdom (so his claim to the throne is voided). You claim you only got as far as the sixth layer (instead of the seventh, which you really reached), tying with your good brother, and declare you're removing yourself from the race for the throne, so your good brother becomes king, and you live a long and happy life (and never have to return to Zeven!).
I finished the game on hard, with zero sexual scenes, other than the forced one at the start where you lose your towel in town chasing the thief.