Aki Hiyami/Plot

Background
Hiyami joined Border approximately two years before Chika Amatori and Yūma Kuga. She eventually joined Ninomiya Unit, rising to A-rank and at one point passing the selection for the away expedition team; however, Mirai Hatohara's inability to shoot others caused first her, then the whole squad to be removed from the force. On May 1, the team dined together at a barbecue restaurant to celebrate Sumiharu Inukai's birthday; shortly afterwards, Hatohara ventured into the Neighborhood with her accomplices, causing Ninomiya Unit to be demoted to B-rank as punishment.

Introduction Arc
Ninomiya Unit presumably takes part in the extermination of all Rads in Mikado City.

Large-Scale Invasion Arc
Due to Masafumi Shinoda preventing B-rank units with missing members from fighting against Aftokrator's forces out of fear of capture, Ninomiya Unit is not deployed.

B-Rank Rank Battles Arc
Ninomiya Unit fights the first round of rank battles on February 1.

Round Two
Since Azuma Unit, Katori Unit, Ōji Unit and Yuba Unit compete in a four-way rank battles in the day division on February 5, and Ninomiya Unit is known to have clashed with Ikoma Unit on that same day, the battle presumably took place in the night division, with Kageura Unit as the third team.

Round Three
On Saturday February 8, Ninomiya Unit competes in the third round of rank battles.

Round Four
On February 15, during the night division of rank battles, the match between Kageura Unit, Ninomiya Unit, Azuma Unit and Tamakoma Second begins in a snowy Cityscape B. Noticing the small number of trion signatures on Radar, Hiyami infers that the members of Azuma Unit are wearing Bagworm and hypothesizes that they might have equipped Grasshopper to outmaneuver everyone else. After Masataka Ninomiya corners Yuzuru Ema, Hiyami confirms his hit. He requests the map of the building the Sniper fled into before reassigning her to supporting Shinnosuke Tsuji. The match ends with Ninomiya Unit in the lead with three points. They retain their position at the very top of the ranking.

Galopoula's Blitz
Since Azuma Unit, Kageura Unit, and Yuba Unit fight in the night division of rank battles on February 19, Ninomiya Unit must have competed in the day division against Ikoma Unit, Ōji Unit and Suzunari First. They continue to rank first at the end of the match.

That night, Ninomiya Unit defends Border's headquarters against Galopoula's blitz. Hiyami presumably assists her teammates until the attack is repelled.

Round Six
Ninomiya Unit fights against Kageura Unit, Azuma Unit and Suzunari First in the night division of the sixth round of rank battles. Kageura Unit and Ninomiya Unit tie at the top with three points. No unit receives the survival bonus due to there being multiple survivors. Following the match, Kageura Unit remains in first place with a point total of 37.

Round Seven
Since Tamakoma Second faces off against Kageura Unit, Azuma Unit and Suzunari First in the day division of rank battles on March 1, it can be inferred that Ninomiya Unit competes against Ikoma Unit and Ōji Unit in the night division.

Round Eight
The following evening, the members of Ninomiya Unit run into Chika, Osamu Mikumo, Kirie Konami and Shiori Usami at a restaurant. Hiyami forbids Konami and Usami to mess with Tsuji before helping him remember what Haruaki Azuma's favorite dish is. When he claims that he was able to converse with Hatohara because she was nice from the start, Hiyami suspects that he is trying to imply that she was not. He states that she was guarded at first, but that she is kind now. When the conversation moves to Hatohara, she remembers that she left right after they went out for a barbecue. Her teammates and she finish their meal and leave before the Tamakoma members.

On March 5, Ninomiya Unit fights the last rank battle of the season against Tamakoma Second, Ikoma Unit and Yuba Unit. Hiyami warns Inukai, who is training with Tsuji, when the match is about to begin. When Chika and Yūma don a Bagworm, Hiyami suggests that they are attempting to escape, although they might also be planning an ambush. She then recommends Ninomiya and Tsuji also go off-radar to avoid Kazuto Tonooka. Chika eventually begins to bombard the remaining combatants, with Hiyami warning her teammates that more rounds are likely to follow. She enhances Inukai's vision so it will be easier for him to intercept the incoming explosives. The match ends in Tamakoma Second's victory, with Ninomiya Unit placing second. The three points garnered put their final score at 44, allowing them to retain their position as B-rank #1.