Persona x Detective Naoto (found 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.  These chapters were specifically serialized in Dengeki Maoh's October 2014 issue, December 2014 issue, and February 2015 issue respectively.
On April 19th, 2022, YouTuber Fitherfith uploaded a video titled "This Persona Manga is Lost Media" in which he asked his subscribers and everyone watching the video for help with finding the missing chapters. Two days later the video "The Lost Persona Manga Has Been (Mostly) Found - Persona X Detective Naoto" was uploaded, in which Fitherfith states that one of his subscribers, Yurizia, sent him a ".rar" file that contained the previously missing chapters, being chapters 13, 15-17, and 19. Surprisingly, the file received also contained an additional chapter, that being chapter 20 which nobody seemed to be aware of or had known about. According to Yurizia, he downloaded all of these chapters from a Flickr account called "juanjoxp07" around 7 years ago.
After the latter video was published, Fitherfith would later receive an additional chapter, chapter 14, from one of his viewers, Montblanc, and would later announce said news on his comment under the same video.
Two months later, on June 17th, 2022, Fitherfith uploaded another video entitled, "The Lost Persona Manga Has Been FOUND (Persona x Detective Naoto)" on which Fitherfith talks about an e-mail he got from the person that used to run the now deleted Flickr account "juanjoxp07". The e-mail contained the missing chapter 18, the final previously missing chapter, bringing this search to a close. Fitherfith would eventually upload every previously missing chapter to a Google Drive link, where everyone can now download the chapters as a ".rar" file.