Kuroyuri (S04E10)

A flashback unveils Ren and Nora's history: long ago, Kuroyuri faces an onslaught of Grimm, spearheaded by a fearsome Nuckelavee, resulting in the tragic loss of Ren's parents. In a moment of crisis, Ren's Semblance kicks in as he witnesses Nora in peril, allowing him to regain his composure and cloak their presence from the approaching Grimm. Back in the present, Ren and Nora come to the alarming realization that the Nuckelavee is now on a collision course with Ruby, Jaune, and Qrow.