Shield

"A defensive Trigger. It's more durable the smaller it is."

- Osamu Mikumo about Shield

Shield (シールド) is the primary Defense Trigger used by all known Border agents. Combatants from Galopoula possess a very similar Trigger, as do some types of Trion Warriors.

Appearance
Shield generates an even, transparent green barrier with no default shape or size. It is most commonly seen taking a hexagonal shape or a round one, but it can also be molded in more complex forms, such as a crystal-like one. Its shape does not need to be regular and can also be convex. Furthermore, it can be modified even after the barrier is summoned. Galopoula soldiers generally summon pentagonal barriers. The lower the surface area, the darker the color will be, mirroring the increase in density. When Shield is activated, a glowing green hexagon appears on the user's hand or wrist.

Overview
It is unknown when Border created this Trigger. Since some Neighbour countries use it, it may be part of the technology that Border acquired in the Neighborhood. Its performance rate has been increased over time.

Abilities
Shield is an indispensable Trigger for all agents, regardless of their class. It allows the user to generate a moderately strong barrier in a location of their choosing, including one's own trion body, and its size and shape can be modified freely. The smaller it is, the higher its durability. It is also more resistant if kept immobile.[BBF Q136] Its ability to be shapeshifted at will, even after it has been deployed, makes it considerably versatile. It can protect only selected areas or the user's whole body from all directions, and even be finely divided. Gunners can spread it around their weapon to fire without exposing themselves, exploiting its transparency. Since the barrier can float on its own, either remaining fixed in place or following one's movements, the user's hands remain free. Shield can also be cast around allies within a radius of approximately 25 meters, although the maximum range fluctuates depending on the user's skills. Multiple users can combine their Shields, juxtaposing them in order to increase the area of defense without reducing their durability too much, or overlapping them for extra localized protection. The act of activating Shield through both the main and the sub is known as Full Guard.

The durability of a barrier is heavily influenced by the amount of trion the user has, positively as much as negatively. In general, it can withstand multiple rounds of Gunner Triggers, and in fact it has contributed to relegating Gunners and Shooters to roles of support. Lightning is the sole Sniper Trigger that can be stopped with a normal Shield. To block an Eaglet shot, on the other hand, it is necessary to focus the barrier to a width of a few inches, which normally requires the user to anticipate the Sniper's target and firing position. However, not even a concentrated Shield can resist Ibis. As for Attacker Triggers, a focused Shield can repel Raygust even when it is accelerated by Thruster as well as stabbing attacks with Scorpion, but not Kogetsu, which it can at best delay for an instant. Trigger users with exceptional trion levels may be able to deflect Eaglet without concentrating the barrier and Ibis with Full Guard. Conversely, a Gunner or Shooter with vast trion reserves can break Shield with a single volley of bullets.

Shield does not interfere with Triggers which lack direct destructive power, and thus it is useless against Lead Bullet. Thanks to his customized Lead Bullet, Miwa can exploit this characteristic of the Defense Trigger to let his bullets go through his own Shield.

Warriors from Galopoula also possess a Trigger similar to Border's Shield. Their version might be more durable since, aside from blocking Viper, it was able to withstand Fūjin's remote slashes with only a few cracks. Like Border's Shield, the barriers create by this Trigger are transparent and can be summoned anywhere in the user's vicinity. It is however unknown if their shape and size can be changed, since all the shields used by Galopoula agents were pentagonal and had roughly the same surface area. Users either have at least two such Triggers in their equipment, or are able to generate two barriers with the same one.

Users
Shield is part of the Trigger set of every A and B-Rank agent participating in Rank Wars, as well as in Yūichi Jin's and those of the members of Tamakoma First, for a total of 94 known users, which makes it the most popular Trigger in Border. The total number of Shield chips, however, is a minimum of 182 as all official agents but 6 have two Shields in their Trigger set. The exceptions are Kyōsuke Karasuma, Osamu Mikumo and the 4 Bagworm Tag users. Masafumi Shinoda has also used this Trigger.

Gatlin, Wen Sō and Ratarikov have also shown to utilize a Trigger very similar to Border's Shield, suggesting that it may be part of the standard equipment of soldiers from Galopoula.

Humans are not the only ones who can use shield Triggers. In Border, dummies can be fitted with Shields to help Shooters practice. Rodochroun, a planet-nation that specializes in the making of Trion Warriors, is able to manufacture models that can generate shields, such as Manberdo Dogs and Idras. The latter are particularly remarkable for their ability to combine their shields to increase their durability, but even the shield of a single Idra can withstand a Kogetsu slash without cracking.

Trivia

 * "Shield" is also the name of one of the seals of Yūma Kuga's Black Trigger. The two are also similar in appearance and functions, and both are more durable when fixed in place.
 * Chelidon can generate circular barriers not dissimilar to Border's Shield, whose number and diameter can be increased or decreased at will.