Sō'unga

Sounga is a fictional sword in the anime and manga series InuYasha. It is the complete opposite of Sesshomaru's inherited sword, Tenseiga, "the sword of life or heaven", and the more powerful form of InuYasha's inherited sword Tessaiga, "the sword of death or earth".

Sounga, "the sword of hell or of world conquest", can summon 100 dead souls in one swing. In the third movie of InuYasha, the combined powers of the Tessaiga and the Tenseiga succeeded in defeating Sounga, which was stronger than either of them alone.

Sounga, unlike the Tessaiga or Tenseiga, was not created by Totosai from InuYasha's father's fang and it is unknown how InuYasha's father came to own it. Also, unlike the other two, Sounga contains the spirit of an ancient evil demon. When held by a human, Sounga takes control of them, and they will kill everything they possibly can, but when held by a yōkai, then Sounga will try to persuade them to do its bidding. But InuYasha's father never let Sounga control him. Saying it was an act of weakness if he let what he should be controlling take control of him. He used the sword to fight Takemaru of Setsuna as a flaming mansion came down upon them.

Afterwards, Inu no Taishi's servants Miyoga, Totosai and Saiya pondered on what to do with Sounga, after disposing of the Tessaiga and Tenseiga. They couldn't give it to InuYasha, as he was merely a baby at the time and neither Sesshomaru, who desired power. Saiya suggested he'd hold the sword off quietly for seven hundred years, placing it in the Bone Eater's Well. But skipping a number of years, the sword ended up in Kagome's family possession.

When InuYasha grasped Sounga, he was taken over, but regained control for a short period of time. To prevent it from harming from anyone in the future, InuYasha went into the past, where it began a reign of blood. It battled Sesshomaru, knowing all of his thoughts when their swords clash. Kagome managed to release Sounga from InuYasha's arm using the prayer beads, causing the sword to fly off.

Picked up by a lesser demon it had previously slain, Sounga went into the netherworld, retrieving Sesshomaru's left arm and then came upon the burial sight of Takemaru, resurrecting him, giving him the arm so he could use the Dragon Twister and a chance for revenge on Inu no Taishou's sons. Grasping the sword, Takemaru gained a demonic appearance and slaughtered an entire castle full of soldiers to resurrect as the living dead. Sounga's spirit guided Takemaru, as InuYasha and Sesshomaru's groups came upon the castle. Capturing Kagome and Rin, Takemaru tried to strike, but Sesshomaru's intervention stopped it. Sesshomaru tried to kill Takemaru with Tenseiga but he was resurrected. But when faced by InuYasha, his desire to protect Kagome filled his power to push Takemaru back. Realizing that his love, Izayoi wanted him to live back then, leaves the living. But Sounga wasn't finished yet and constructed a body for itself to fight, opening a portal to the Netherworld that would encompass the living world. Sounga fought against InuYasha and Sesshomaru, who battled it individually, only making it stronger. But they combined their Backlash Wave and Dragon Strike to destroy Sounga's body, sending it into the netherworld, where it can't harm anyone.

Special abilities

 * Dragon Twister: Sounga most powerful attack, and more powerful than Tetsusaiga's Bakuryuha, Souuga summons a large, violent, and powerful tornado that destroys, or kills everything in its path. Myoga described this as the attack of a dragon from hell.
 * Sheath of Sounga: Kept Sounga dormant for what seemed like seven hundered years. Saiya inhabits the sheath, whom advised Myoga and Totosai to throw him with Sounga sheathed into The Bone-Eater's Well. Like the sheathes of Tetsusaiga and Tenseiga, it has powerful defensive capabilities.
 * Resurrection: When Sounga is in control of a "Lesser" yōkai, he can bring back a corpse from the dead, and control it, or give it free will. Mindless corpses are filled with deadly liquefied miasma.