Endsinger (Lotus Wars #3) by Jay Kristoff
Synopsis adapted to keep spoilers down (warning, above link has a spoilery summary):
Yukiko and Buruu, mind-bound Stormdancer and thunder-tiger, have returned to the Kage Rebellion, ready to continue the fight against the Lotus Guild, their poison, and their puppet Shogunate. Their allies are dead, demoralized, betrayed, and ripe for failure. Their enemies continue to grow in strength and number.
Yukiko and Buruu will need new allies if they are to defeat their enemies. Luckily, they both know where they can find some – if old hurts can be healed, secrets laid to rest, and new ties forged in the face of betrayal.
As the earth splits asunder, as armies destroy each other for rule over an empire of lifeless ash and the final secret about blood lotus is revealed, the people of Shima will learn one last, horrifying truth.
There is nothing a mother won’t do to keep her children by her side.