The Girl that Lives with Dragons (How to Train Your Dragon/Percy Jackson)

After the battle and Hiccup became chief, he thought he would finally get some rest. Not possible. A girl shows up, riding a Screaming Death, one of the untrainable dragons, during the dragon races. They try to follow her but lose her. He goes back home. He tells his mother about it and it turns out that the Greek gods exist. Not only that but he is a demigod. His father was a blessed by Jupiter and his mother is a daughter Athena. Him and the people in his academy start following the people on flying horses when they lost the girl again.

Percy and his friends had just rescued a girl with a white dragon that she calls Laughter. She calls it a screaming death. They can tell why. She manages to escape before she is claimed and they go after her. It turns out that Nico has taken a liking to this mysterious girl. She flys over the ocean on her dragon so they follow on Pegasi. She opens a portal and they end up on an island. They follow the girl until they lose her. They see some more people on dragons following.

Andra was a daughter of Poseidon and her mother a daughter of Nike. She was born on Berk and was a month old when her town was attacked by Whispering Deaths. Her mother was killed by an arrow that missed the dragon. A screaming death found and looked after Andra until she was able to ride a dragon. She was able to ride the screaming death and learnt how to speak dragon. She named it Laughter because it seemed to laugh a lot. She opened a portal and ended up in a camp. They tried to look after her and train her to fight. She already knew how and beat all of the campers. She then ran away with campers on flying horses and a horse that could run on water following her.