The barrier drone was a specialized UAV deployed by the rogue super-submarine Alicorn during Osea's Operation Fisherman. Barrier drones carried an onboard electromagnetic generator that produced a shield similar to the Arsenal Birds' Active Protection System.
The origin of the barrier drones is unknown. By September 14, the Alicorn carried a large number of barrier drones when Osea began hunting the submarine in the Spring Sea to halt an attack on Oured. The Alicorn launched the barrier drones during the battle to protect the submarine from incoming fire. Trigger destroyed the submarine's ballast tanks, leading Captain Matias Torres to fake a surrender.
While Torres readied the Alicorn's large rail cannon, the submarine launched a swarm of barrier drones to protect the rail cannon. Trigger weaved through the shields and damaged the railgun, causing its shot to miss.
The barrier drone featured a distinctive design completely unlike most other UAVs previously observed in Strangereal. Its physical appearance resembles a flying saucer; it features a hexagonal frame with six large rotors to keep it aloft and, if desired, stationary at a certain position. An electromagnetic emitter is present at the center of the drone. When activated, the emitter creates a small electromagnetic shield around the drone that blocks all incoming weapons. A swarm of barrier drones activating their shields at once helps protect a specific unit such as the Alicorn from enemy fire. The drones appear to be single-use only, as once the Alicorn dives, the drones drop into the ocean.