Dark Box (広暗い箱の底から Hiro Kurai Hako no Soko Kara) is the 160th chapter of the Prison School manga, serialised in Weekly Young Magazine on December 1st, 2014 and published in tankobon format in Volume 17 on June 5th, 2015.


Kate tells Mari that if she guess that is inside the box, she will open it, before calling her a bluff. However, Mari takes quickly a French encyclopedia before pronouncing thief in French and suggest that Kate look up the word because she said it. She notes the marker placed on the page and the good quality of the dictionary as counter to Kate's denial. Mari finally states that her underwear that Kate had stolen is inside the box. Risa tries to open the boys's room, but it boarded, which lead Gakuto and Shingo to think that Mari's break out plan has 'sprung into action'. Mari reveals to a hesitant Kate she knows since a long time ago she was stealing her things after asking her to open the box. Mari divines that Kate want her to found out she was stealing because Kate is in love with her. Kate denied it and hesitate to open the box, but Mari suggests that she don't want to be separate from her.

Mari says next that she will give Kate the bra that she is wearing if she open the box but Kate then engages her in a sumo fight, sending Mari to the ground as she states again that she is wrong. Mari ask why if she don't like her she put her underwear in a treasure box, as the box broke in the fight, revealing underwear to Kate's horror.



  • The chapter title is a cultural reference to Japanese psychological horror film Dark Water.


Prison School by Akira Hiramoto
Volume 1:
Volume 2:
Volume 3:
Volume 4:
Volume 5:
Volume 6:
Volume 7:
Volume 8:
Volume 9:
Volume 10:
Volume 11:
Volume 12:
Volume 13:
Volume 14:
Volume 15:
Volume 16:
Volume 17:
Volume 18:
Volume 19:
Volume 20:
Volume 21:
Volume 22:
Volume 23:
Not in Volumes:
Non-Canon Chapters
Fukukaichou Gambaru:
Anime Promotion:
Other Series:
Other Series:
  • Fukukaichou Gambaru
  • Agonashi Gen to Ore Monogatari
  • Me and The Devil Blues
  • Yarisugi Companion to Atashi Monogatari
  • Sono Tomodachi no Gimon Ari
Community content is available under CC-BY-SA unless otherwise noted.