Our Last Crusade or the Rise of a New World, Vol. 7 (manga) — Kei Sazane

Determined to protect Sisbell, Iska faces off against a mysterious witch who can manipulate gravity. Yet for all the duel's intensity, it's the conflict brewing among the Nebulis sisters that he needs to worry about…Tensions were already high between Alice and Sisbell, but when Elletear, the oldest of the three, gets involved, this sibling rivalry starts to really heat up! Somehow, Iska finds himself at the heart of a dispute which promises to be more fierce than any war he's ever served in...