S4·E10 Kuroyuri

Ren and Nora's past is revealed through a flashback: years ago, Kuroyuri is attacked by Grimm, led by a Nuckelavee, and Ren's parents are killed. Ren's Semblance activates when he sees Nora in danger, which calms him down and hides their presence from the Grimm. In the present, Ren and Nora realize that the Nuckelavee is headed towards Ruby, Jaune, and Qrow.