Alrighty, by tomorrow, I'll have a blood-themed
zanpakutonamed sword/shield item, and I'll find a nifty spellcasting/binding feat. Promise! Do you care much about the dramatic portion? Like, could I draw an ethereal athame from my heart, slashing it across my chest, thus forming a shield from the blood-mist (actually ethereal/arcane energy) issuing forth from the cut and growing thicker (more potent as I grow stronger/our soul-bind becomes greater, perhaps, but I'm trying to think of a proposal that isn't too strong...) as more of my own/my foes blood is spilt? Even if it's just a redder shield as it progresses, not necessarily a higher AC.
It'll probably be a sword, that was just an illustration example; I'd go shield if I thought that giving up my shield spell was a smart choice for a 16 AC spellcaster.
I'm also now reading through tome of magic; fun book, wish I'd seen shadowcasters and the nocturnomancer before I'd started building this guy (thematically, it's almost more perfect), but I'm not doing that to you, Venn. Also, I'm too lazy to.