With the concept of summoning sentient familiars, what if said sentient familiar, just so happens to be the dark lord? The Dark Lord, weakened while performing his duty, went for a stroll after a long three thousand years of work. Eager to finally touch grass and enjoy the great outdoors again, he practically skipped in his haste to taste freedom...only to be kidnapped by the ankle at a summons.  Our poor Dark Lord couldn't help but grumble as his long-overdue vacation slips away. This was not how he planned his retreat would go. (The Dark lord is not edgy or evil, kind of a slightly chaotic neutral. He's born as the element, with none of the personality. Like the saying of the knife is not evil, only the one who wields it is. )