Viper

"Ballistics for which you can choose the trajectory: Viper."

- Shiori Usami about Viper.

Viper is a Gunner Trigger.

Appearance
Once shot, Viper appears as a luminous trail that, due to its properties, often resembles a zigzag. The size of each bullet is directly proportional to the amount of trion the user has. Gunners fire Viper bullets through different types of gun-shaped Triggers, whereas Shooters form a trion cube that can be divided in smaller regular polyhedrons, their size and shape depending on how many are created at once.

Overview
The origins of this Trigger are unknown. It was first used by Shooters only, until firearm Triggers were invented.[BBF Q156]

Abilities
The main feature of Viper is that its projectiles can travel along trajectories the user has programmed in their mind before shooting. This property gives it more complicated flight paths than any other bullet Trigger, including Hound, but its destructive power is lower than Asteroid's. Although the number of patterns available is theoretically infinite, due to Viper being the most difficult Gunner Trigger to master agents learn and preprogram only a few useful trajectories. Two of them are Pattern A and Pattern B. Pattern A causes the bullets to scatter after a few meters before converging on one point. It allows the user to hit enemies hiding behind flat, durable shields. Like Pattern A, in Pattern B bullets start moving in a straight line before fanning out in multiple directions. This set of flight paths makes it possible to quickly target multiple opponents, shoot behind corners and to use feints by pretending to attack one enemy and then redirecting the bullets to hit other targets.

Certain Shooters, however, are capable of creating new patterns each and every time they use this Trigger. To do so, a keen sense of spatial awareness and the skill to visualize something that does not yet exist are required.[BBF Q148] Rei Nasu and Kōhei Izumi are the only two users who can efficiently exploit this capacity in combat. Hyuse was hinted to be able to do the same, although he is still inexperienced. This capacity grants them unparalleled flexibility and permits them to fight efficiently regardless of the presence of obstacles, as they can simply program the bullets to avoid them. They can even use them to their advantage, curving the flight path of the projectiles out of sight so as to lead the opponent to miscalculate their position. Other tricks at their disposal include the ability to target multiple enemies with the same trajectory by making it go through multiple of them, so that even if the first dodges the attack, another will be hit. Since the bullets can change pattern at any moment, avoiding them is very difficult if the user can predict how the opponent will move. This strategy can be used to suddenly focus a seemingly scattershot attack on only one point, tricking the target into expanding and hence weakening their defense before breaking through with concentrated fire. A user who can control Viper freely can employ luring tactics to lead the enemy into thinking they are vulnerable after shooting, whereas they have directed their bullets to come back and bombard the area around them.

When combined with Meteora, Viper creates the composite bullet Tomahawk, which retains the explosive properties of the former and the ability to travel along predetermined patterns of the latter. The merging of Asteroid and Viper takes the name of Cobra.[BBF Q143] Its characteristics are still unknown.

Users
See also: Viper Users

With merely 8 known users, 3 Shooters and 5 Gunners, Viper is by far the most unpopular Gunner Trigger. Among the Gunners, 3 channel it through an assault rifle and 2 through at least one handgun. The three agents who can use this Trigger to its full potential, Kōhei Izumi, Rei Nasu and Hyuse, all use it as Shooters, and are the only ones to do so, although Hyuse admitted he still needs to practice. It should be noted that the list above excludes those members of branches who do not participate in Rank Battles.

Trivia

 * Like other Gunner Triggers, Viper may have been named after a missile, the AGM-80 Viper, whose system offered fire-and-forget performance. Alternatively, it may be derived from a rocket, the FGR-17 Viper.
 * The viper is a family of venomous snakes. Snakes have many vertebrae which allow for increased flexibility, which is similar to how this Trigger is flexible in changing trajectory.