The Crybaby Boy's Vow is the 9th overall episode of Tegami Bachi
In the memories, Gauche insisted on working more deliveries despite the risk of losing his heart for the sake of curing Sylvette's disability. The last memory of Gauche was the time before he headed for the capital and his first encounters with the group called Reverse. Lag promises to find Gauche and bring him back to Sylvette.
Soon, Sylvette hands Lag Gauche's shindanjuu for him to use, per her brother's wishes. Back at the Bee Hive, Largo evaluates Lag's performance and makes him a full-fledged Letter Bee. However, Lag explains his dream is not to become just a Bee; he wants to become Head Bee someday, where no delivery of letters is impossible.