Heckler & Koch PSG-1

The Heckler & Koch PSG-1 is a semi-automatic sniper rifle used by the Tokonosu Prefectural Police Special Assault Team (S.A.T.). It is used by Rika Minami while she is stationed at Tokonosu Offshore International Airport.

Overview
The PSG-1 is a sniper rifle manufactured by Heckler and Koch that is used by many armed forces around the world, particularly in an anti-terrorism role. The way it was found in the manga seems pretty legit as Rika was assigned for anti-terrorism. In fact, real life SAT has several of these rifles in their arsenal, which explains how Rika was able to get one.

Plot
The PSG-1 is only seen once when Rika uses it to eliminate "Them" on the runway to clear the way at the airport. Although it is not clear yet, she might actually carry it around as one of her arms, if not her standard issue firearm.