lvl 4 character or lvl 4 Hexblade
It replaces the "Summon Familiar" ability gained on your 4th level of Hexblade.
That said, arcane resistance is an untyped bonus of 8-9 vs all Spells and SLAs, and Mettle lets you completely negate effects with a save, so those first few levels are definitely not wasted.
If you do take Hexblade, You may need to do some early entry shenanigans to get the 2nd level arcane casting needed for Anima Mage.
Also, if you want Ur-Priest level abuse but arcane, you can use Darklight Wizard.