Name: Tsuchinaga Hiyori
School: Arius Branch School
Club: Arius Squad
Grade: 2nd Year
Age: 16
Birthday: January 8
Height: 155 cm
Hobby: Collecting magazines

A student belonging to the Arius Branch School's special forces unit, the Arius Squad.
She gives a melancholic impression from her appearance and serves as the squad's sniper.
She always wears a dark, faint smile, frequently utters negative and self-deprecating words, and is a pessimistic individual with low self-esteem, servility, and timidity.

Unable to believe in a happy future, she holds the pessimistic view that "life is suffering," and has a habit of saying things like "It hurts, doesn't it?" and "It's painful, isn't it?" to both herself and others. Taken out of context, this might sound sadistic, but in reality, this is also self-deprecating muttering.
On the other hand, she often falls into self-loathing and lets out a screaming cry like "Uwaaaaahn!", and contrary to her sullen behavior, she has wide emotional swings and intense reactions (she also makes that crying sound when moved to tears).
Even in the narrative, she gives a much more comedic impression compared to the other three who maintain a consistently serious atmosphere.
She also possesses a rare type of resilience born from resignation; she negatively interprets any support or service from others as "they're going to demand payment later" and despairs on her own, but then, thinking "it's the end anyway," she recklessly gets greedy and places additional orders, showing she is surprisingly pushy and, in a good way, tenaciously holding onto life.
These patterns, like "Uwaaaaahn! I'm done for, aren't I!? I'm going to become ○○, aren't I!? Might as well, since it's the end anyway..." are collectively known as "Hiyori Construct" and are frequently joked about as an internet meme.

Unusually for an Arius student who typically wears a mask, she does not wear any kind of face covering. She has something like a scarf or shemagh wrapped around her neck, so perhaps that serves as a mask substitute?
However, in her swimsuit version, she only wears sunglasses, so it seems Hiyori alone has no intention of actively hiding her face.
In Arius, she has a baby face alongside Atsuko, but her chest is quite large. With a height of 155 cm, she is not particularly small, and it seems she has a relatively good physique despite growing up in harsh nutritional conditions.
Incidentally, her midsection is somewhat flabby, and in the Memorial Lobby she shows a belly button that is squashed in shape while saying, "I'm self-conscious about the shape of my belly button."
This complex is thought to be influenced by her love of the aforementioned fashion magazines, the presence of someone nearby who constantly shows off a perfect belly button and abs, or perhaps the environment she herself is in.
Also, within the squad, she seems to be doted on like the youngest child, with Saori and Atsuko treating her with a somewhat indulgent attitude. On the other hand, because of her usual behavior, the unavoidable evaluation that "if it came down to choosing between herself and her comrades, she'd pick herself" left her feeling quite wronged and shocked.
While the remaining members of the squad harbored hatred for them after their defection, Hiyori alone was not particularly blamed—whether that was because she was inconspicuous, or she was seen as a low-ranking member without decision-making authority...

Her mental state aside, her survival skills when alone are surprisingly clumsy and unreliable.
The model for her unique weapon "Identity" is the NTW-20. The 20mm caliber is confirmed from the description.

In her standing sprite and pre-battle SD character, it is stored in a huge gun case and cannot be confirmed, but its appearance can be seen in the unique weapon screen and when using her EX skill.
Incidentally, the NTW-20 is an extremely heavy firearm weighing about 26 kg, normally requiring it to be disassembled and carried by two people, but in her EX skill cutscene, she carries it undismantled inside the gun case on her back along with a huge backpack about her own height as she rushes in.
She seems to be in love with someone, and is slowly getting closer to that person.