Blue Notes Blues (chapter) is the 23rd overall chapter of Tegami Bachi Manga
Zazie is shown with Wasiolka collecting post from Mrs. Hannah, whom tells him that the town's overall letters that have piled up were stolen. She doesn't know what's going on, but there is no known leads as to whom did it.
Meanwhile, Lag and Niche discover a cave near the lake, but are told by the townspeople not to enter. They take Lag and the others back to town, where Lag asks about Noir, to which, they confirm that Noir went to the cave, which is a path leading to Blue Notes Scale and the holy site. The Mayor, Harry Tonov, warns Lag not to enter as he will be punished severely.
He gives Lag a book that explains the history of how the townspeople suffered when the geothermal energy around the town was stolen, leading to dead crops and widespread illness. A pregnant woman named Celica became greedy and decided to drink the water of the underground lake to gain immortality. Accompanied by Celica's return, the town returned to normal. However, Celica became quiet and eventually gave birth to twins before she died, which are the children of Maka.