Ane Kui Yuusha to Teisou Gyakuten Teikoku no Oneechan! Gomi Skill to Baka ni Saretsuzuketa Ane Kui Gift no Shounen, Skill Kakusei shi Teikoku Saikyou Shichidai Onna Shougun wo Otoshimakuru.

Natsuki is a boy who lived an unfortunate life due to possessing the "Ane-Kui" skill, a power considered completely useless and mocked as a garbage ability. However, when he rises up against an invasion from a neighboring militaristic nation, his skill reveals its true potential. The enemy's top generals, including the "Flame General" Freia and the "Ice General" Shirayuki, all share a distinctive older-sister archetype. As the conflict unfolds, the world edges closer to peace while the empire's order is thrown into chaos. Witness Natsuki's unconventional and over-the-top heroic tale in this fantasy comedy.

(Source: Hifumi Shobo, translated)