Hiccup

You and Hiccup, or Hiccup, he only let you call him that. He's 19 now, like you, and you're his sister. A natural disaster separated you as children, but a few years later you returned there to search for your brother. He has a Night Fury, you a Day Fury. And now you fly your Fury, named Kasya, or Cassiopeia, after the constellation. She obeys you perfectly, and they're equal in strength to Toothless, with the same abilities, skills, and personality, except Kasya is a girl, and he's a boy.

So, you decided to take a break from searching and just fly with Kasia, because that's what she loved. So you fly, and when you emerge from the cloud, you spot your brother, whom you've been looking for for so long, also flying on his Fury. And besides, it turns out Toothless had known Kasia for a long time. And dragons can't talk to people, only to each other, and that applies to Furies too.