Sokyoku(PITZWIL100)

The Sokyoku (双殛, Twinned Punishment) is a massive halberd that's used by the Soul Society to execute Captain-level criminals, for crimes such as treason. It's stationed on top of Sokyoku Hill.

Overview
When not in use, the Sokyoku is pointed up toward the sky, sealed and locked into place by several large brown ropes, constructed by the Kido Corpse. In order to release it, the Kido Corpse is required, as it is their advanced Kido Spells that seals Sokyoku. When the Sokyoku is activated for an execution, it bursts into flames, the heat of which can be felt all over the Soul Society. The blade will then pierce the criminal--as it does, the last thing they can see is a giant falcon of some sort made entirely out of fire, until it vaporates their soul.

The blade itself was created by Shigakuni Genryusai Yamamoto, by taking his own fire-type Zanpakuto, Ryujin Jakka, and expanding it into the blade. However, due to the Sokyoku constantly feeding on the Reishi in the air of the Soul Society, the fire in the blade is said to be far more powerful than Yamamoto's Bankai's flames.

Plot
In an attempt to turn Momo Hinamori and Toshiro Hitsugaya against one another, Sosuke Aizen tricked Momo, via a letter, that Toshiro was planning on using the Sokyoku to destroy the Soul Society. During Rukia Kuchiki's execution, Ichigo Kurosaki came in just in the nicki of time, and personally stopped the flames. Right after he did that, Shunsui Kyoraku and Jushiro Ukitake worked together, using the Shihoin Clan Shield, to destroy the Sokyoku.

When Hinote Sonodeddo Banbutsunoreichou betrays the Soul Society, and kills Sentaro Miyamoto, the former's elder sister, Shitoyakahan Sonodeddo Banbutsunoreichou, abandonds the Soul Society, and fuses the new Sokyoku with her own soul, in order to gain the power needed for her to kill her brother.

Appearances In Other Media
In Bleach: Shattered Blade, it is revealed the destruction of the Sōkyoku broke the seal which was imprisoning a powerful Arrancar named Arturo Plateado. At the same time, the Sōkyoku shattered into several pieces, even one of which could augment the spiritual power of its holder. Arturo plots to collect all of these shards and use their power to decimate Soul Society.

Trivia

 * In the Anime, the Kidō Corps used hand signs to release the Sōkyoku.