Haku is Koa's adoptive grandmother, bhy whom she's affectionately called Yaya Haku.
Haku lived on her island on her own, until one night she went fishing and found a baby. A little girl, crying, helpless, in the middle of the sea. Haku couldn’t leave her there, so she took her home, ready to give her away when the time came. But she couldn’t do it. The baby grew happy, strong, free, but Haku’s thumb.
She has to be very strict with Koa. The girl doesn’t know. but she has a very important task in the island. Yaya will tell her when she grows up, but until then, she just trains Koa and waits for her to be ready. She sees herself in Koa: a brave child, careless and without fear, but very uneasy and hard to manage.