This is all my speculation: Rykell's power to call forth winter weather is truly frightening (anyone who's endured a week long winter bomb storm can agree) and I think Galatea's power to call forth spring and new growth was instrumental in moderating his power and stabilizing his emotional state, after how he was treated by his own family. When Galatea left him (either by death or forced separation), his grief and rage literally tore up the country. The royal family put those bonds on Rykell and forced that pact on him to literally save the kingdom from being destroyed. To ensure the kingdom's safety, they sent him out to hunt monsters, as a way to make use of his grief and rage against the world. And that is why he couldn't take Maybelle with him. No place for an infant daughter when you're hunting monsters. He left her with his older brother's family, paying them handsomely to properly raise her.
Maybelle has probably inherited her mother's magic calling forth spring and new life. I think that she'll grow exponentially, and manifest great magic, just like her mother. Her father will probably dote on her excessively, teaching her all he knows, and seeing her as a manifestation of her mother's love and final gift to him.
