Part of Seragaki Aoba’s existence, Ren is an entity born from Aoba’s power who maintains the balance between Aoba and the other entity inside him. While he normally takes the form of a black Pomeranian / Japanese Spitz, Ren is later revealed to have a human form as well.
Meet Hong Kong-ese cosplayer, Terashima Iris! I wish my puppy had a human form too! That would be great! And a lot easier to figure out what he’s thinking. Thanks to Terrence for sending this in!
Source: Terashima Iris on World Cosplay