You haven't noticed? If she takes enough damage she goes from happy to angry (she can also switch back and forth between the two manually with her A+K, but it damages her a little). When she's angry, she sounds different, a lot of her attacks change and she's a lot faster, but every attack does a tiny bit of damage to herself. Once she does enough damage, she switches back to happy Tira. It's a great addition to her character and it makes her a lot more fun to play as.