Ailyn, a top student with excellent grades but doesn't know the meaning of her life. 
Yumeki, an orphanage girl who shines brightly in her quest to become her ideal self. 
One day, a monster named "Sonster" suddenly appeared in front of them, swallowed Yumeki and then disappeared out of the air. To learn more about Sonsters, Ailyn joined the secret organisation "Sonsterity"...