Ra should be fine. You have SQ active to pretty much negate the 50% shield.
If I hit him to ~20% health will he have to use Brave Resistance before he can attack me, or will he skip straight to Last Belief? If he has to waste time dispelling my buff or using gravity, which I think is how it works, then I can do it. Maybe. I did the math on it just now, and on average I drop him to around 20% with a common Kali board and max levels. I don't want to take the time to figure out how being underleveled effects this, but it might still work if I can conserve enough actives.
Edit: Got enough stones for one more foolish Halloween pull, saw a silver egg and got excited (lol) and...
-Izanami
God dammit, I don't want to complain about getting such a great monster, but seriously, that's three now. Give me the thing I actually want for the same rarity plz.