Red XIII isn’t playable in Final Fantasy 7 Remake, Square Enix has confirmed.
Speaking to VG247, Final Fantasy 7 Remake co-director Naoki Hamaguchi said the iconic red wolf / lion turns up in the game at one point as a guest character, but he’s controlled by the AI. You can’t control him yourself.
Explaining the move, Hamaguchi said because Red XIII joins the party later in the story, there’s not enough time to flesh him out.