toaru hikuushi e no seiyaku
とある飛空士への誓約, lit. Oath of a Certain Pilot is a Japanese light novel series by Inumura Koroku and illustrated by Morisawa Haruyuki. It took place after Toaru Hikuushi e no Koiuta. Currently, since 2012, 4 volumes were published by Shogakukan under their Gagaga Bunko imprint.