I promise.

"Go to the Heroes, they'll protect you. I promise."
I promise.
Those words changed Kioko's life. They shaped her future.
I promise.
You can't break your promises. Broken promises are what will lead hero society to its destruction. That doesn't stop Kioko's sister from making a promise she can't keep.
She swears she won't make the same mistake as her sister. She'll keep her promises. She'll protect everyone.