Concept art and game design Practice

I want to create games, so this is some practice of making a game concept.

The story is that the player plays as this cute character.
One day she finds a magical cave. In this cave, she finds another world. The animals living in this world are creatures she's never seen before. In one quest she notices an overgrown broken house, which implies humans might have lived there before. In this world, she meets this old dragon. The dragon claims he is this world's protector and he gives the player quests that help her with the story.
This world is dying from a parasite that is killing everything alive. She gets scared it might spread to our world and wants to stop it. Eventually, she realizes it's something the dragon had created and she was helping him destroy his world. In the last quest, she uses something she got during a previous quest and destroys this world.