Pre-Series Timeline

List of events dated proior to the start of the series

10+ years ago

 * Yūgo Kuga, Sōichi Mogami, Masamune Kido, Masafumi Shinoda, and Takumi Rindō found Border. They ally themselves with the Neighborhood nations Aristera, Meson, and Dexio. Yugo Kuga invents the Rank War system.

9 years ago

 * Yūgo Kuga teaches Yūma (6) "The 3 Teachings".
 * Reiji Kizaki's father is killed while protecting a child, allegedly by Neighbors.

5 years ago

 * September 22: Yōtarō Rindō, Prince of Aristera, is born.
 * Aristera falls when an unnamed nation attacks. The remaining royalty flee to Japan, where Border shelters them. Cronin, Ruka, and Yōtarō join Border. Border Combatants Shin Kazama, Kengo Soma, Tetsuya Umesaki, Hibiki Taira, Sōichi Mogami, Manabu Kai, Kaede Namekata, Rintaro Chihiro, Motoki Suzumura, and Ibuki Wakisaka all die during the conflict.
 * Sōichi Mogami uses his remaining Trion to create the Black Trigger, Fūjin, before his death.
 * Mato Kujō leaves Border to become a civilian.

4 years ago

 * Spinthir attacks Calvaria.
 * Motokichi Kinuta, Eizō Netsuki, and Katsumi Karasawa join border, presumably as executives.
 * First Large-Scale Invasion

3-4 years ago

 * Yūgo Kuga dies while saving Yūma (11).

2 years ago

 * Sōya Kazama (19) offers Shirō Kikuchihara (14) a place in Kazama Squad, to which he accepts.

1 year ago

 * Calvaria defeats Spinthir after years of war.
 * Kyōsuke Karasuma and Shiori Usami transfer to Tamakoma Branch for unknown reasons.

8 months ago

 * Tetsuji Arafune quits being an Attacker and becomes a Sniper (8 months prior to Round 2).

6 months ago

 * Sunday, April 28: Rinji Amatori tells Osamu Mikumo about his plan to enter a gate into the Neighborhood with collaborators.{{ref|name = c82p9|c = 82|p = 9
 * Wednesday, May 1st: Ninomiya Squad go to Jujuen for Sumiharu Inukai's 18th Birthday.{{ref|name = c178p8|c = 178|p = 6}}
 * Thursday, May 2nd: Rinji Amatori, Mirai Hatohara and at least two other collaborators are confirmed to be missing after attempting to enter a gate to the Neighborhood.{{qref|name = c82p11|v = 10|c = 82|p = 11|e = 36}}
 * Osamu Mikumo enrolls in Border, 6 months before Yūma's and Chika's enlistment.{{Ref|name = bbfp=270-271|db = bbf|p = 270-271}}

Start of Series
See: Timeline