LonelyKoi resembles a Taisho Sanshoku koi fish, with a predominantly white body, an orange leg and arm, and a single black arm. His body is also marked with small orange and black spots. He has fish tail, gills. Koi also has a scar on his left cheek. Koi is easily frightened or fearful, a result of the abuse and trauma he endured from GoodPuffer and AngeredFish. He had problems with trusting anyone, and has difficulty understanding others due to his prolonged isolation in the lab.