The Lost Song is a visual novel about how an air force member Marina encounters a singing merman Zeru while cruising the island and how this brings enormous changes to her boring life. Become the heroine Marina and see things through her eyes, listen through her ears and make choices through her heart. By facing herself, Marina will be able to witness the change of her and Zeru's future.

There are multiple choices and two endings in this visual novel. By making certain choices, the true ending can be unlocked.

In the Steam version, two bonus illustrations are added at the end of each endings and can be viewed again through the in-game gallery.