Taihai (たいはい, Literally meaning "Decadence") is a chain-whip like weapon and one of the three lost weapons of the Era of the Warring States that are currently in the possession of members of the organization, Seidou.
Taihai's construction resembles a unique type of whip-blade with faint purple, swirling patterns etched into each serrated blade, tiny spikes which dig into the user's arm, drawing blood and unerringly stealing Haru's chakra.
Every time Haru strikes someone with this weapon, it not only injures them, but siphons off their life force, healing him in the process as Taihai is continuously sapping him of strength. Taihai, being in essence a chain, increases Haru's reaching range dramatically. While wall-running, Haru can hook onto lamps jutting from a wall in order to gain more momentum to continue further along the wall as well as poles sticking out serve a similar purpose, except it is used while jumping, Taihai can also pull switches too far away to use by hand.