Kenji is a quiet shopkeeper who has taken over and transformed the family store. His only problem is his sister's daughter, whom she entrusted to him before leaving. But one day, the police come to question him about the disappearance of one of his customer's family. The only clue is a mysterious symbol drawn next to a door. Kenji doesn't feel particularly concerned until Donkey, a childhood friend, asks him if he remembers that same symbol. Kenji then explores Donkey's life, his past, and that of the group of friends he was part of in his youth. He soon discovers the existence of a clandestine organization led by the enigmatic Ami, which uses the symbol linked to Kenji's past as a rallying sign. This passage appears to be a synopsis of the manga series "20th Century Boys" by Naoki Urasawa. The story revolves around Kenji, a convenience store owner, who becomes entangled in a mystery involving his past and a secretive organization. The narrative skillfully weaves together elements of mystery, friendship, and conspiracy, creating an intriguing plot that spans different time periods in the characters' lives. Source: https://www.bedetheque.com/serie-4518-BD-20th-Century-Boys.html

Manga - Seinen : Mystery, Science fiction, Thriller

Seinen manga (青年漫画) is an editorial category of Japanese comics marketed toward young adult men. In Japanese, the word seinen means "youth", but the term "seinen manga" is also used to describe the target audience of magazines like Weekly Manga Times and Weekly Manga Goraku, which write on topics of interest to male university students and workingmen. Seinen manga is distinguished from shōnen manga, which is for young boys, and seijin-muke manga [ja], which are intended for adult audiences and often contain explicit content. Some seinen manga like xxxHolic share similarities with shōnen manga. Seinen manga can focus on action, politics, science fiction, fantasy, relationships, sports, or comedy. The female equivalent to seinen manga is josei manga. Source: https://en.wikipedia.org/wiki/Seinen_manga