Sidereae is a senior high school student who became a 'Dreamer' after meeting a mysterious man named Oneiroi. It was after his father's funeral when he met Oneiroi, who mysteriously appeared in his room.
He was responsible for convincing her to become a 'dreamer', someone who can travel into different worlds in a form of dreams while experiencing different lives. Oneiroi convinced her to become one and find the truth about her father's mysterious death.
Sid who's desperate in escaping reality because of her father's death agreed after hearing Oneiroi's honey-like words and is determined to find the truth about her father's death.
However, becoming a dreamer has a consequence and that is, the more she dreams the more she loses herself, making her to forgot her goal and move further from reality.
Mathieu who noticed the changes in his childhood friend Sid began to observe her more closely and tried to not leave her alone. For he's the one keeping her from getting swept away from reality.
Will Mathieu succeed in keeping her and help her to regain her sense of reality? Or will Sid be able to fight the current of her fantasy, and lose herself into oblivion?