User blog comment:DeathGodPrayer/Talk About What You Want!/@comment-4311395-20120513013550/@comment-98.77.246.197-20120513224803

Issei originally wanted the slime to be his Familiar but the rumor is that Tiamat will become his Familiar and he is supposed to meet her in Volume 14 of the Light Novels. Tiamat is the only active Female Dragon KIng other than Tannim from the Devils and they list her power to be at the level of Maou.