It won't help against non-living opponents. But you could do UMD with a wand of Draconic Malice, for anything that's living.
Take a few levels of anti-paladin.
One of the foolhardiest follies imaginable is to build a rogue/ninja, which already roll over to creatures immune to sneak attacks, around a mechanic a large number of enemies are also immune against.
Keep in mind aura of corwarise removes fear immunity. It doesn't remove immunity to mind effecting, so most undead and vermin will still be immune.
The best way to deal with fear immunity? Get another means of dealing sneak attack which doesn't rely on scaring the unscarable. Dirty tricks (a ninja can be good at these with the redirect force ninja trick), or turning invisible (also a ninja specialty), or whatever.
Hey all so I'm building a mythic ninja, im using the shuriken, shatter defense build, now generally im pretty happy with it, (it WotR so most of the enemies are demons) but i get the feeling im going to have to fight some fiendish undead or mind controlled paladins at some point. so my question is how the hell do i strip someone of fear immunityWhen the game grants "immunity" to anything as a class ability, it is generally very stingy about removing it, because it means there will be massive amounts of butt-hurt nerd-rage.
and no taking a three level dip into anti-paladin isn't an option again do to the aforementioned paladins.
(Paladins with improbably crappy will-saves? K...)
Anyway, I assume this is all to keep Shatter Defenses fueled.
-- If it's just about keeping damage going, why not explore other means of gaining it besides sneak-attack? I.e., as a ninja you are a charisma build (I'm guessing it's your second-highest stat). So, rather than levels in anti-paladin, try levels in real paladin. You saves in your "weak" ones shoot up nicely, and a few times a day you'll get a nova attack-bonus versus a particularly annoying evil. You probably already have a charisma headband and meditation crystals to fuel your Ki.
Three levels of pally + Silver Smite Bracelet vs. evil-outsiders or undead or evil dragons = 3x/day Smite Evil for +Cha to hit and +14 damage in the first attack per round and +7 for others in a full-attack. Melee or Ranged (i.e., why, hello there, Flurry of Stars).