Reiji Kizaki/Plot

Background
9 years before the start of the series, Kizaki's father was killed while protecting a child as a rescue worker. This death inspired Kizaki to make himself stronger due to the doctrine his father implanted into him: "rescuers who don't return alive fail."

Black Trigger Capture Arc
Kizaki first appears when Jin and Karasuma try to trick her into thinking that Osamu, Yūma, and Chika were his siblings. He dismisses the joke. Later, he is assigned to Chika a mentor. When he has her go for target shooting, he is immensely shocked at the amount of trion she has. He also helps Osamu train physically, as fitness was important for fighting in a trion body.

Border Enlistment Arc
He does not appear in this arc, but Azuma mentions that he had a lot of faith in Chika to have taught her that Snipers need to run after shooting their target.

Large-Scale Invasion Arc
He, along with the rest of Tamakoma First is dispatched to Osamu's location by Shinoda. He helps fend off the Rabbits along with the rest of his unit. When Hyuse and Viza arrive, he fights Hyuse with Karasuma. It is during this confrontation that he figures out that Lampyris used magnetism as its gimmick. After Karasuma and Osamu take the C-rank trainees to flee, he and Konami prepare to fight the duo, but Viza sends Trion Soldiers towards the civilian evacuation areas. Kizaki orders Konami to pursue them and takes on the Neighbors himself. He uses Spider and Meteora to set up traps to defeat his opponents, but is eventually overcome by Viza's far superior Organon. It is revealed that prior to the invasion, Jin had ordered him to not go full-out against his opponents, and to accept defeat when it came. He Bails Out, much to Yōtarō's disappointment at the fact that he did not use Full Arms.