Dezember Zwolf (ディツェンバー・ツヴォルフ Ditsenbaa Tsuvorufu) is one of the 12 Month Demons and one of the 4 Great Demons of the Demon World. He is the main antagonist of Senyū for the anime and Chapter 1. He is a secondary antagonist onwards.
- Hates liars and justice
- Has 6 personalities/bodies based on dice numbers.
- Shadow magic
- Has the ability to physically split into 6 different personalities.
- "Dezember Zwolf" means "December 12" in German.
- He is the "darling" of Guilty Justice.