Yuri+Kanojo: Kossori Kiss shite
百合 + カノジョ : こっそりキスして · ゆり + かのじょ : こっそり きすして
est. Rough estimate based on volume count, reprints and magazine — not an official figure
External databases: MADB · AniList
How to compare editions, collected volumes and ISBNs / Sources, updates and corrections