Tegami Bachi: Letter Bee

One day, while on a delivery to a certain mansion, Lag is asked by Ray Attlee the owner of the mansion, to search for the person who sent a picture-letter to her. Ray says that the pictures in the letters reminded her of her hometown, and gave her the will to continue to live on and fight her illness. Lag, after being called a "Letter Specialist" by Ray, decides not to rely on his shindan that allows him to see the heart contained in letters, and does his best to search for the sender. He discovers that the paints used to paint the letters have some connection to Ray's hometown, and then...