A Bittersweet Smile

This story is about Lily Shuu and May Yuki, a girl incapable of smiling, and Lily with a promise to help her smile. However, May moved away the day after their meeting, leaving their promise unfulfilled. Six years later, they are reunited, and Lily has the chance to fulfill her promise to make May finally smile. But can she keep the secrets about what happened the day after their meeting?