Arnold is a demon who was summoned to this world when Toby accidentally read a cursed book aloud, bringing along Eck in the process too. He is the drummer in his band, Ghost Nails, which you can find the logo for embroidered on his hat. Toby is the one who put the design on there, officially creating the logo for their band, with Eck as a singer.

Arnold and Eck and both dating romantically and have been doing so for thousands of years, which can tire Arnold out at time, but they get along like a couple of old school buddies. The two of them now live with Toby after the summoning, causing them to be trapped within a certain radius of the book they came from, Toby carrying it with him as he is now also bound to it as a result.