Persona x Detective Naoto (partially lost manga adaptation and cancelled third Tankōbon volume of "Persona 4" role-playing game; 2012-2015)
Persona x Detective Naoto is a spin-off novel and manga of Atlus's 2008 game, Persona 4, featuring the character Naoto Shirogane. The novel was written by Natsuki Mamiya and published on June 10th, 2012 under the Dengeki Bunko label. A manga adaptation illustrated by Satoshi Shiki followed soon after in the Japanese magazine, Dengeki Maoh, and ran from December 27th, 2012 to January 1st, 2015.
Over the course of its run, the first 12 chapters were collected into two Tankōbon volumes under the Dengeki Comics NEXT label, both of which are easy to find and purchase online. However, chapters 13-19 never got released in a Tankōbon format, only being serialized in Dengeki Maoh. Despite this, Volume 3 was slated for a June 27th, 2015 release, and has multiple listings and a confirmation from Dengeki Maoh. 
Scans for chapters 13-16 exist online, but no scans for 17-19 have surfaced. These chapters were specifically serialized in Dengeki Maoh's October 2014 issue, December 2014 issue, and February 2015 issue respectively.