Kogetsu/Senkū

"Kogetsu Optional Trigger: Senkū. A momentary lenghtening of the blade's reach through a trion expenditure. The swinging blade is most deadly at the tip."

- Senkū's description

Senkū is an Optional Trigger exclusive to Kogetsu, including its spear variant. An attack carried out using this Trigger takes the name of Senkū Kogetsu.

Appearance
Senkū has no physical manifestation outside of its effect on Kogetsu, whose blade it extends. Due to the speed of the swing, the attack can appear only as a ribbon of light originating from the blade. Should Kogetsu be a different color than the standard one, the blade will be changed back to its default color after Senkū is used.

Overview
The origins of this Trigger are unknown. Due to its function, it cannot have been created before Kogetsu.

Abilities
Senkū allows the user to temporarily extend their Kogetsu's blade by consuming trion for vastly increased reach and cutting power. The power of the slash peaks at the tip of the blade. The extension is inversely proportional to the duration of the effect. the majority of Attackers keep it activate for 1 second, resulting in a range of 15 meters, but Tatsuhito Ikoma can comfortably execute a Senkū slash with the activation time being a mere 0.2 seconds, which causes the blade to extend up to 40 meters. This extreme application of Senkū can cut cleanly through large Escudo barriers, but even an ordinary activation has proven capable of cleaving through a minimum of five smaller Escudo, some within a few meters of the Senkū user, without difficulty. Kei Tachikawa used this Trigger to bisect two Rabbits vertically despite the very durable armor on their head and back being capable of resisting two simultaneous Scorpion slashes without taking any significant damage.

Skilled Senkū users like Ikoma and Tachikawa are able to swing an elongated Kogetsu twice within one same activation, while Yōsuke Yoneya was able to strike five times in a row with his Spear, although it is possible he simply extended the activation time or it is an advantage given by his custom Kogetsu. Another notable application of Senkū is the one demonstrated by Masafumi Shinoda, consisting in pinpoint attacks which resemble Mantis more closely than a proper slash. He also displayed the ability to avoid obstacles, although whether he did so through sheer skill, in conjunction with Gen'yō, or through a Trigger/Border Triggers#Customization|customization]] is currently unknown.

Shinoda, Tachikawa and Ikoma are consistently shown sheathing their Kogetsu between attacks, and the act of drawing it has been repeatedly recognized as a telling sign of the wielder's intention for activating Senkū — although there are also instances of it being unequivocally activated when Kogetsu was already out of the scabbard. However, whether the act of sheathing and drawing Kogetsu has any use remains unconfirmed. The speed at which Kogetsu extends and shrinks is likewise unknown.

Due to being an exclusive optional trigger, Senkū must be equipped on the same side of the slots as Kogetsu in one's Trigger set, however it can be activated even if two Triggers are already in use.

Users
See also: Senkū Users

There are 27 known users of this Trigger among official agents, including Yōsuke Yoneya, who activates it through his Spear. Masafumi Shinoda also has Senkū in his Trigger Set. This is excluding Tatsuhito Ikoma is hailed as the best Senkū user in all of Border, but Shinoda and Kei Tachikawa are also worthy of note. Members of branches who do not participate in Rank Wars are excluded from the count.

Trivia

 * The way Kogetsu is often unsheathed right before using Senkū is probably a reference to, where one draws their sword from the sheath only moments before striking.
 * Similarly, Ikoma was taught and has always sheathed his Kogetsu when doing his special Senkū, so it is possible that anyone who uses it has to learn Iaido to pull it off correctly.
 * In the English translation of Chapter 154, Yuu Kunichika heavily implies that Senkū can be activated only while drawing Kogetsu; however, the original text makes no mention of it.
 * Kyōsuke Karasuma, Shūji Miwa and Kotarō Tomoe are the only three official agents that have Kogetsu but not Senkū in their Trigger set.