Ryuu no Kyoudai

Emi, a depressed girl who lost her mother, moves to Enoshima, where her aunt lives. Dragons fly around Enoshima, and she has been able to see them since she was a child. One day, Emi sees a large dragon and a small dragon that she once saw with her mother descend on the island. She chases after them and finds that there are a human brother and sister...

(Source: Natalie, translate)