As Corrin is technically a member of the Hoshido Royal family, his siblings were devasted when he was taken from them. But none were moreso affected than Hinoka.
Hinoka was always attached to Corrin, and when they got kidnapped, she blamed herself for not being able to prevent it. Thus, she trained to be a Sky Knight so she could one day find Corrin.
Because of this, Hinoka's personality changed dramatically, she went from a softer soul to one hardened and determined to protect her family and save Corrin. Even when he (potetnially) returns, she is still fiercely determined to protect him and ensure he never gets taken away again.
Regardless of your path, Hinoka plays a big role in each game in Fates, her fate though is hugely tied to your decision. And her passion can be either be a huge boon, or a huge disadvantage depending on the side you choose.