Shiori Usami/Plot

Background
Before joining Tamakoma Branch, she was part of Headquarters. Two years before the start of the series, she was the operator of Kazama Unit during its early years. She moved to Tamakoma Branch around a year before the series began.

Black Trigger Retrieval Arc
Usami introduces Osamu, Yūma, Chika to Tamakoma Branch. There, she mentors them about Rank Battles, Triggers, and other topics in Border.

Border Enlistment Arc
When questioned by Yūma as to why he is with Yōtarō, Yōsuke explains that he's babysitting "that little bastard" for her, while Yōtarō tells Yūma that Yōsuke and Shiori are cousins. Yōtarō also explains that Shiori and Kyōsuke were both HQ members until a year ago. Later, she appears at the meeting, aiding Replica in his explanation of the Neighborhood.

Large-Scale Invasion Arc
She is the operator of Tamakoma First during the invasion, giving directions to Karasuma and Osamu so they could reach HQ and battle their opponents.

B-Class Rank Battles Arc
She acts as the operator of Mikumo Unit. She helps them plan for their battle with Arafune Unit and Suwa Unit.