Since he was the team hacker and rarely experienced actual combat, Achates himself used the weapon so infrequently that by the time of the mission to SORA Gas & Electric he'd forgotten he had it. Nevertheless the guards at the main hangar forced him to surender it.
When Amphinomus and Camilla defeated the guards, the micropistol was the only weapon to survive the battle. Amphinomus held onto it until the fire fight in the wind tunnel, where he gave it to Protesilaus after the latter's pistol ran out.
Protesilaus attempted to use it against Sir Beys during the fight next to the primary generator, but Sir Beys knocked it out of his grasp. After defeating Protesilaus and Amphinomus, Sir Beys wielded the pistol himself and threatened to kill Dolon with it. Hippolytes suddenly stopped him by sniping the pistol from afar. (Nietzsche's Soldiers 2)