Ten no Ryuu Chi no Sakura

Sakura Karukaya liked her life: she was just a high schooler who loved rhythmic gymnastics, being raised by her older brother and sister. However, both of her siblings were hiding secrets about themselves and Sakura that would make her realize that the world around them was not what it seemed. Now, with the help of a mysterious dragon-king named Yoiyami, Sakura will have to confront these forces and the power within her if she wants to rescue her beloved brother and sister.

(Source: Which Scanlations)