Chappy is Vigne's pet back in the demon realm, when she first found him, he was still a pup and one year after that, he has grown massively.
When first found, Chappy was a small puppy and later in the current story timeline, he has grown to the size of his owner's house. He has mostly dog-like appearance with the horns similar to a mountain goat's and fangs appearing out of his mouth, light pink fur with white around his chest to lower stomach and red tuft that looks like a mohawk over his head and flaming red tail.
Chappy has 2 expressions in his grown-up state, first is his scary expression that makes him looked like he is going to devour what he sees and the second one is his cute face that originally appeared since he was a pup.
Since he was hurt and separated from his parents when he was a pup, Chappy was brought by the Tsukinose family and become loyal to them, especially Vigne.
Chappy may look intimidating when Vigne met him back home but it maybe because he is excited to see her finally back instead. Since he is still one-year old, Chappy's personality is very much similar to a usual puppy. He is playful, happy and curious as he chase after butterfly like a pup does.
Despite his looks, Chappy is innocent, harmless and friendly, although his young age and character paired with his size is prone to cause trouble for others, as he did to the Tsukinose's house when Vigne tried to take him for a walk.
- Vignette April Tsukinose: Since Vigne is the one who found him and nurse him back to health, Chappy is very loyal to her, although his young personality and massive size tends to cause trouble for her in when he has grown up. Vigne however, truly cares for him as she remembers him on her way home despite her reaction for the unexpected surprise when finally reunited with him (she even thought he was a monster first). Chappy also earned his name from Vigne.
- Mrs. & Mr. Tsukinose: Both of them loves Chappy like their daughter does, but Mrs. Tsukinose maybe more active in taking care of him since Mr. Tsukinose does not appear when Vigne came home (possibly at work) and unlike her daughter who was horrified by Chappy's growth, she is completely fine about him, she is also the one who calls Chappy as "Chappy-chan" signifying they have strong relationship.
- Satanichia McDowell Kurumizawa: They met each other once when Chappy was chasing butterfly and accidentally met Satania and Alexander while they were playing. Satania was slightly scared of him but refused to give up and thought that Alexander is still better than him. Unfortunately, the dragon pup chose to cower (although a smart move) by pretending that he is dead.
- Alexander: They met when both owners are taking them to have fun and play. When Vigne introduced Chappy to Satania and Alexander, the hell hound breathed his fire in excitement over meeting them. While it was accidental, the incident unfortunately traumatized Alexander to which he plays dead when Satania told him to do a counter attack (trick) so that the hell hound would not harm him.
- Vigne states that Chappy is an demon beast (魔獣 Majū lit. monster) but his exact species was not stated, so no official species type is known for him. However, his dominant dog/wolf like appearance and fire breathing shows that he is likely a hell hound.
- Since he is a doglike demon beast, he is one of two dog type demon beast in demon realm, the other one is the Cerberus. Coincidentally, Vigne used Cerberus too to help her sleep by counting them in her mind, also both beasts are fire breathing.
- Chappy's from one year ago was very small, he was small enough to fit in a soup bowl and was smaller than Alexander. Now however, he has grown to the size of a house. Vigne even stated that he grew too much.
- Unlike Alexander, Chappy has a known good relationship with his adoptive family, Mr. Tsukinose was the one who suggested to take him home, Mrs. Tsukinose is his caretaker while Vigne is away and probably the closest to him and Vigne is his real owner.
- While his name is Chappy, the sound he makes is "Chiii". Also, his voice is very high-pitched like when he was still a pup despite how much he has grown.