Kogetsu

"Next, the most popular, all-purpose blade: Kogetsu, "Arc Moon"."

- Shiori Usami

Kogetsu is an Attacker Trigger.

Appearance
Kogetsu's appearance is akin to that of a, with a luminous yellow blade made of trion, but without a tsuba (guard). A black-blade Kogetsu was also used by Kō Murakami in Round 7 of the B-Rank Battles.

Overview
Until a few years before the start of the series, Kogetsu was the sole Attacker Trigger in existence. Its origin seems to date back at least to the days of Old Border.

Abilities
Mirroring its popularity, Kogetsu is considered the best-made Attacker Trigger out of the three, as well as the most balanced. It boasts high offensive power, and it is more durable than Scorpion, making it possible to intercept the attacks of other blade Triggers a great many times without the blade risking to break. It is the Trigger of choice of aggressive Attackers and All-Rounders. A single swing of Kogetsu can generally break a focused Shield, including one created by Yūma's Black Trigger, but not those generated by Idras. Unlike Scorpion and Raygust, Kogetsu cannot shapeshift; however, its blade can be temporarily extended by combining it with the Optional Trigger Senkū, or its shape manipulated with Gen'yō, another Optional Trigger.

Much like Gun Triggers and Raygust's handle, Kogetsu can be turned off in order to use other Triggers without the need to dispel it, and even without putting it back in its scabbard. As long as it remains off, the blade will not be able to cut anything. However, since, unlike Scorpion, it cannot be manifested or withdrawn at will, a blunt Kogetsu can prove to be a burden. To avoid this inconvenience, it is possible to dispel both the blade and the scabbard and conjure them again when needed at the expense of some trion. A new Kogetsu blade can be materialized even without destroying the scabbard, which can prove useful should the user be disarmed or the blade become unfit for use. While inside its scabbard, Kogetsu can be broken with just one Senkū slash.

One of the few downsides to Kogetsu is its weight. If it is not wielded with both hands, the user may be thrown off-balance, or underperform as a result of their swordplay getting slower. However, agents who have reached Master Class routinely show to be capable of holding it with only one hand without difficulty. A very circumstantial drawback of Kogetsu is that, like the other Attacker Triggers, or at least Raygust, it has a luminescent blade; however, its color can be changed to black with the help of an engineer, eliminating the glow and thus rendering Kogetsu invisible in the darkness.

Users
See also: Kogetsu Users

Many Old Border agents used this Trigger. Currently, there are 28 known official agents (B-Rank and above) with at least one Kogetsu in their Trigger set, including Hyuse; if Yōsuke Yoneya's modified Kogetsu is included in the list, the number goes up to 29. Among HQ personnel, Masafumi Shinoda, believed to be HQ's strongest Trigger user and Kei Tachikawa's swordsmanship teacher, deserves to be mentioned as well. A recurring user who is not an official agent is Hidehide Hinoe. The list excludes those members of branches who do not participate in Rank Battles.

The Kogetsu user with the most Solo Usage Points is Kei Tachikawa, the no. 1 Attacker and solo combatant. Yūichi Jin, Raizō Terashima and Kirie Konami are notable among the former users of this Trigger.

Trivia

 * According to the author, sometimes, when a Kogetsu suddenly disappears, it is because he has forgotten to draw it.
 * The concept of a black Kogetsu was teased by the author in the official databook prior to its appearance in the series.