These were the top 20 selling manga in December 2021, according to NPD BookScan:

  1. Chainsaw Man Volume 8 by Tatsuki Fujimoto
  2. Jujutsu Kaisen Volume 13 by Gege Akutami
  3. Demon Slayer: Kimetsu no Yaiba Volume 2 by Koyoharu Gotouge
  4. Chainsaw Man Volume 1 by Tatsuki Fujimoto
  5. Jujutsu Kaisen 0 by Gege Akutami
  6. Jujutsu Kaisen Volume 1 by Gege Akutami
  7. Chainsaw Man Volume 2 by Tatsuki Fujimoto
  8. Attack on Titan Volume 34 by Hajime Isayama
  9. Toilet-Bound Hanako-kun Volume 1 by Aidairo
  10. Attack on Titan Volume 1 by Hajime Isayama
  11. Chainsaw Man Volume 3 by Tatsuki Fujimoto
  12. Jujutsu Kaisen Volume 2 by Gege Akutami
  13. Death Note Black Edition Volume 1 by Tsugumi Ohba and Takeshi Obata
  14. Tokyo Ghoul Volume 1 by Sui Ishida
  15. Deserter: Junji Ito Story Collection by Junji Ito
  16. Jujutsu Kaisen Volume 3 by Gege Akutami
  17. Kaiju No. 8 Volume 1 by Naoya Matsumoto
  18. Toilet-Bound Hanako-kun Volume 2 by Aidairo
  19. Haikyu!! Volume 1 by Haruichi Furudate
  20. Demon Slayer: Kimetsu no Yaiba Volume 4 by Koyoharu Gotouge

Source: The Fandom Post