Holy cow... Phoenix with just her fists is one thing, but Phoenix taking up a sword is just absolutely stunning.
Sirin's continued 'childish' personality really just makes this story so much sadder. Yes, she's using the powers of unimaginable evils to enact her vengeance...But her heart and mind, truly, are still that of a scared, lost child. She isn't versed in combat, doesn't seem to know much of the world (After being locked up and practically tortured through experimentation who would...), and yells "Cheat!" every time something she didn't expect happens. It often seems apparent she doesn't even know what she's truly capable of.
She's likely past redemption as a result of her actions, but it's such a shame she had to fall victim to the power and will of the Herrscher.