Akuma to Keiyaku: Kare no Ijiwaru na Aishikata
アクマと契約 : 彼のイジワルな愛し方 · あくま と けいやく : かれ の いじわるな あいしかた
est. Rough estimate based on volume count, reprints and magazine — not an official figure
External databases: AniList
How to compare editions, collected volumes and ISBNs / Sources, updates and corrections