The Battle of Traitors - S1.E23

Reiga kidnaps Yuki and uses him to lure Luka and the Zweilts into his territory. Takashiro discovers Reiga's whereabouts and sends Luka and the Zweilts to rescue him. Hyde is held back by Hotsuma and Shusei, Elegy is held back by Tsukumo and Touko, and Cadenza is held back by Kuroto and Senshiro, leaving Luka to confront Reiga and save Yuki. During the magical battle with Reiga, Luka is badly injured. Then Reiga blasts Yuki, intending to kill him, but Luze who addresses Luka as "older brother" arrives and stops the blast because his understanding was that Yuki is essential to their plans.