Fukabuka to, Shinigami Katarite Shuuchaku
深々と、死神語りて執着 · しんしん と しみがみ かたりて しゅうちゃく
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