Upotte's portrayal of the Finnish RK-95 cold weather rifle, a derivative of the AK-47/AKM.
RK-95 is known exclusively by the name sako. She is fairly tall, looks older than she is, blonde haired, red eyed and has very long elflike ears.
Sako is a self-worshiping sadist, who throughout the manga bullies, tortures and even attempts to kill other members of her class. This... Unique behavior has made her quite popular in fandom circles.