40代が、こんなにしんどいなんて聞いてなかった = I didn't know 40's is so hard.
よんじゅうだい が こんなに しんどいなんて きいてなかった
est. Rough estimate based on volume count, reprints and magazine — not an official figure
External databases: MADB
How to compare editions, collected volumes and ISBNs / Sources, updates and corrections