Lost Letter is the 20th overall episode of Tegami Bachi
Lag and Niche return to the Bee Hive and find Zazie recovering from injuries sustained by a gaichuu attack. Aria questions Zazie on the letters he lost during the attack, citing the Letter Bee's responsibility to find and deliver them.
Soon, Lag fires at the gaichuu to no effect as it easily dispels his shot from an opening in its body. Steak manages to retrieve the letters but the group end up in danger. Zazie arrives to fight the Gaichuu but does not care about the delivery of the letters. Lag attacks the gaichuu and it reveals Zazie's flashbacks, showing the Bee to have lost the letters while unable to defeat the creature with his shindan.
Lag, Niche and Zazie work together to destroy the gaichuu. Afterward, Lag offers to deliver the letters for him but Zazie insists on going with him, saying it was his original responsibility to do so in the first place. He tells Lag he didn't explain to Aria about his own inability to defeat the gaichuu as he wanted to do it himself.