Tegami Bachi, Volume 17 Late Hire Chico

A New York Times best-selling sci-fi fantasy series with heart.
Amberground is locked in darkness. A man-made star casts only a dim light over the land. The pitch-black wilderness is infested with Gaichuu—colossal insects with metal exoskeletons. The Gaichuu make travel between the cities of Amberground extremely dangerous. But thankfully the Letter Bees, a brave corps of messengers, risk their lives in order to keep the hearts of Amberground connected.
Lag now knows what he has to do to save Amberground: unite the five children born on the mysterious Day of the Flicker. And his latest delivery may lead him to vital information. But meanwhile Lag has to cope with his brash new partner, Chico, who insists that nothing will stand in her way to becoming Head Bee!