Tessaiga

was a sword wielded by the hanyō Inuyasha. It was the opposite of Sesshōmaru's inherited sword, the Tenseiga. Out of the two, Tessaiga was "the sword of destruction", while Tenseiga was "the sword of life." Tessaiga has a mind of its own, it has been seen guiding Inuyasha, such as wanting to be drawn or giving him advice; the same goes for Sesshōmaru's Tenseiga.

History
The swordsmith Tōtōsai created the Tessaiga from a fang of the daiyōkai the Inu no Taishō, the father of Inuyasha and Sesshōmaru. In its 'docile' form, the sword looked like a regular (and rather battered) katana. When wielded properly, it transformed into a weapon roughly the size of a car bumper that somewhat resembles a falchion. The Tessaiga only transformed if the user cared for humans and had yōki, this means that humans can never wield it because they do not possess yōki. The Tessaiga had the power to slay 100 demons in one swing by striking the Kaze no Kizu, it also had the ability to absorb the technique or skill of a strong yōkai that was defeated with the sword.

The Inu no Taishō used the Tessaiga to steal Shishinki's Meidō Zangetsuha technique, but because of the danger the technique bore the Tenseiga was created to contain it. When the Inu no Taishō died a barrier was put on Tessaiga to prevent full yōkai who hated humans from being able to use it, and the sword was hidden inside his grave in the world between the living and afterlife. Sesshōmaru searched for the sword some time after his father's death, but had no luck in finding it, finally he asked Inuyasha about the Tessaiga's location. After a series of events both brothers travel to their father's grave to claim the Tessaiga. Sesshōmaru was unable to touch the sword, while Inuyasha was not only able to wield it, but used it to defeat Sesshōmaru. After the battle Inuyasha became the master of Tessaiga and began to use it to aid him in battle. During a battle with the Thunder Brothers it was revealed that the sheath can 'summon' the Tessaiga. Tessaiga can also protect it's master by putting a barrier around him, however the barrier the sword produces seems to only work after the attack has hit him.

Inuyasha learns how to transform Tessaiga and use its Kenatsu quickly enough. He didn't learn to use it's true power to slay 100 demons until Sesshōmaru (who had a human arm with a Shikon fragment in it so he could wield Tessaiga) briefly stole the sword and used it himself. He showed the power by summoning 100 demons and slayed them, even to the point of destroying the mountain in one slash. Even after seeing the power, Inuyasha didn't know how to use it, until he accidentally used it to prevent Miroku from being eaten by yōkai when he couldn't use his Kazaana. Naraku blackmailed Sango into stealing the sword for him by threatening Kohaku's life. After she & Inuyasha battled, it was then that Inuyasha was able to retake the Tessaiga back. Inuyasha finally discovered the secret of slaying 100 yōkai was the Kaze no Kizu and learned how to use it during another battle with Sesshōmaru. Inuyasha begun to use the Kaze no Kizu as his finishing move afterwards.

However, in a confrontation with Goshinki, an incarnation of Naraku, the Tessaiga was broken in half. Tessaiga breaking reveals that it kept Inuyasha's demon blood under wraps. The sword's creator, Tōtōsai, was able to repair the Tessaiga, but in doing so he used one of Inuyasha's fangs. The result is that Tessaiga now became dependent on the strength of Inuyasha himself, rather than his father's - making the weapon heavier and more difficult for Inuyasha to wield. However, at the same time Tessaiga also became much sharper and sturdier, able to match a sword forged from the tusk of Goshinki, the same Oni that originally shattered the sword. After much training, Inuyasha learned how to use a greater power based from that of the Kaze no Kizu to take out a powerful enemy, a technique known as Bakuryūha.

In the third movie of the InuYasha franchise, the combined powers of the Tessaiga and the Tenseiga succeeded in defeating the Sō'unga, the sword of world conquest, which was stronger than either of them alone.

Gaining New Powers & Abilities
As Naraku became stronger, Inuyasha began to use Tessaiga's useful power/ability-absorbing ability to strengthen the sword with new much stronger- powers and abilities to help him defeat Naraku. Seeking a way to break Naraku's barrier, Inuyasha went to defeat the barrier-keeper of the bat demon tribe in order to obtain a technique to shatter barriers; instead Inuyasha ended up helping the barrier keeper, Shiori. To thank him, Shiori allowed him to cut her orb- the source of barrier/shield-erecting power - and Tessaiga gained the power and ability to break through barriers.

Subsequently, Tessaiga absorbed Hōsenki's Kongōsōha technique, but as with Red Tessaiga the power was gained by Inuyasha doing something to help others. In this case Inuyasha saved his friends from Naraku's miasma instead of trying to cut Hōsenki and strengthen the sword. Kōngosoha allowed Tessaiga to cut down Naraku's stronger barrier and cut down enemies strong enough to withstand the Wind Scar.

The next power Tessaiga absorbed was the yōki absorption from the demon sword Dakki. Unlike the previous two abilities, Inuyasha had to actually battle and destroy the sword to acquire the power. Since Dakki could absorb yōki it nearly took all of the Tessaiga's powers, but Inuyasha used his sword to destroy Dakki and gained the ability to absorb yōki in the form of Dragon-scaled Tessaiga. Inuyasha didn't master the Dragon-scaled Tessaiga right away unlike the previously acquired powers. Being a hanyō limited the amount of yōki Tessaiga could absorb before the yōki backfired on Inuyasha and injured him. By using Dragon-scaled Tessaiga to absorb the senki from a Seimiekan sent by Naraku, it purified the yōki it absorbed thereby stopping the regurgitation, but in the manga, he cut Nikosen's Life Force Stalk with the Dragon-scaled Tessaiga.

By doing this, Sesshōmaru and Tōtōsai told Inuyasha that he did not know the true meaning of Tessaiga and took a shortcut instead of mastering the form. After training, Inuyasha learned to see yōketsu of yōkai; by cutting it with Dragon-scaled Tessaiga he could destroy the source yōki thereby killing the yōkai.

The final ability Tessaiga gained was the Meidō Zangetsuha from Tenseiga. During a battle between Sesshōmaru and Inuyasha, Sesshōmaru willingly broke Tenseiga on Tessaiga to give it the Meidō Zangetsuha technique as their father had intended. The technique allowed the user to send their enemy directly to Hell. In the final battle with Naraku, Inuyasha fully mastered the technique and it changed into an attack that cut an enemy and then sent what it touched directly to Hell, and pulled the remains into the cuts.

General appearance
At first glance when not in use, the Tessaiga appeared to be nothing more than a battered katana with a heavily chipped and rusted blade with the hilt's fabric tearing away. When transformed, the blade turned into an over-sized dog's fang, fitting for its name. The cross guard turned into a large patch of fur similar to a dog's also. In the later chapters and episodes, the blade not only became slightly larger, but changed colors and transformed according to the abilities it absorbed.

Katana Form

 * Anti-Yōkai Barrier: The Inu no Taishō placed a barrier within the Tessaiga that will burn pure yōkai that attempt to touch it. In the canon manga, Tōtōsai (being the sword's creator) is the only yōkai who can both hold and activate the Tessaiga without harm. Humans are capable of holding the Tessaiga in its untransformed katana state, with the sword's barrier protecting them from harm. Because Inuyasha is a hanyō, he is capable of both holding the Tessaiga without harm and activating its true form once he begins to show compassion for humans.

True Form

 * Kenatsu: was the special ability that allowed the Tessaiga to cut opponents without touching them, surrounding the blade in yōki. Inuyasha used the ability befe he learned the Kaze no Kizu.
 * Kaze no Kizu - Wind Scar in the English dub: Special attack that killed 100 demons with one strike with a massive wave of demonic energy. Inuyasha took some time to master this technique, and didn't even know of its strength at first, until Sesshōmaru showed it to him. It was gained by sensing the fissure or scar between two demonic forces. After his battle with Ryūkotsusei, Inuyasha learned to put his own power into the attack so the fissure appeared around Tessaiga's blade and could be triggered instantaneously. Until Inuyasha gained that ability, the Wind Scar was not very useful against Kagura since she can change the demonic winds so they didn't clash and create a fissure.


 * Bakuryūha - Backlash Wave in the English dub: Tessaiga's ougi (or ultimate technique). Used the opponent's strong demonic forces and unleashed the Wind Scar at the right point, the demon's energy will be reflected back with the added power of the Wind Scar. The power of the original attack was amplified many-fold. Gained by Inuyasha defeating Ryūkotsusei and reflecting his power back at him. However, two requirements were needed in order to implement the Backlash Wave. The first was that Inuyasha can only reflect pure energy attacks. The second was that his own demonic aura must be much stronger than his opponent's or the Backlash Wave will not form. It was shown in the InuYasha movies (though never in the anime) that the Backlash Wave can be activated by relaying the power of Kagome's Sacred Arrow.



Red Tessaiga

 * Barrier Shattering: Gained from Shiori's orb for saving her from her grandfather and his bat yōkai, this technique completely shattered barriers. When in use, Tessaiga's blade turned completely red to signify its usage. In this state, the blade was able to break barriers, allowing Inuyasha to reach his enemies. Though it could cut through Naraku's barrier at one point, it could not following the events of Mount Hakurei; however, Inuyasha failed to realize this even after failing to break Hakudōshi's barrier with it. It was also ineffective against a holy barrier, such as Hitomiko's. Note:  Interestingly, when Sesshōmaru fought Inuyasha when Tenseiga and Tessagia were about to become a single sword, the Diamond Spear Blast was ineffective against the barrier of Tessaiga's sheath (which Inuyasha used to defend himself) but the Red Tessaiga was able to destroy the barrier.
 * Enhanced Wind Scar: While in this state, Tessaiga can still produce the Wind Scar, but adds the ability to break barriers to the blast; it was used to break barriers from long distances. Inuyasha had used it against Naraku and Hakudōshi, failing with both; it only worked once on its own against Naraku.



Diamond Tessaiga

 * Kongōsōha - Adamant Barrage in the English dub: Attack gained from Hōsenki after Naraku had used a shard of the jewel to corrupt him and caused him to attack Inuyasha. The diamonds were able to pierce Naraku's stronger barriers, thus even the Infant, Hakudōshi and Byakuya's barriers would also be sundered. Also, the attack cannot be performed simply for the diamonds, which are valuable in the modern era. Inuyasha was also capable of combining this technique with his Wind Scar. Oddly, it had no effect on the barrier of Tessaiga's sheath during the battle that joined Tessaiga and Tenseiga.
 * Adamant Backlash Wave:  As seen in InuYasha the Movie: Fire on the Mystic Island, Inuyasha was able to unleash the Backlash Wave with Tessaiga in this form; he relayed the attack with Kagome's sacred arrow. When used, streams of diamonds head towards the target, in this case the combined form of the Four War Gods, and pinned it in place. When Inuyasha swung his sword, the diamonds broke apart and headed towards the enemy with blasts of energy.



Dragon-scaled Tessaiga

 * Yōki Absorption: Having defeated Dakki, Tessaiga gained the ability to absorb an opponent's yōki (demonic energy) directly. Inuyasha, being a hanyō, limited the amount of yōki the sword can absorb before it backfired on the user. After being bathed in the Great Holy Demon Spirit's demonic energy, the regurgitation stopped.
 * Yōketsu Cutting: After realizing the true nature of the Tessaiga was to cut, Inuyasha learned how to see yōketsu (whirlpools of demonic energy) and used the Dragon-scaled Tessaiga to cut it, instantly destroying a normal yōkai. Beings created of many different yōkai, like Naraku and Mōryōmaru, have several yōketsu, which means cutting them will destroy parts of their body and prevent regeneration of the destroyed parts; however, the Fuyōheki proved to be a nuisance as it hides yōki, preventing Inuyasha from seeing where to strike. It can also cut the large amount of yōki emitting from a strong yōkai, which can be fatal. If Inuyasha cuts his own yōketsu, the power will flow back into himself and Tessaiga, making the yōketsu grow; it can even devour the Path to the Underworld if uninterrupted.



Black Tessaiga

 * Meidō Zangetsuha This technique was attained when Sesshōmaru's Tenseiga broke on Tessaiga. The original technique formed a direct path to Hell by creating a giant circle that can suck in anyone in it's path. It can also be used as an escape from a Meidō one was already in; doing so will transport the user and anyone else back to the normal world if they were already in a different dimension. However, exit location is not set; Inuyasha used it to reach both the closed-off path between eras in the Bone Eater's Well and the Sacred Jewel itself.
 * Meidō Blades: When Inuyasha completely mastered the Black Tessaiga, the Meidō Zangetsuha changed to symbolize the Tessaiga's true nature, a sword that cuts. The new Meidō was able to create a single black blade, or several black blades, that not only cut a opponent, but have their remains sucked up into the path. Thus the technique keeps the original ability intact while also adding the Tessaiga's cutting nature. It seemed to be stronger than the regular Meidō, as it was able to tear apart Naraku's final form, which was impervious to the original move.

Tessaiga's sheath
Can deflect or resist demonic energy attacks with the barrier used to contain Tessaiga's power. However, it can only withstand a limited number of attacks. The sheath was capable of resisting any amount of offensive force; however, if that force was used continuously then the sheath would crack. This was why it was able to hold off Sesshōmaru’s Sōryūha since it was an attack that was only unleashed once, but couldn’t hold off Hiten’s thunder attacks which were of weaker power than the Sōryūha, since he was unleashing them constantly. The sheath can also summon the Tessaiga to itself, as seen when Inuyasha was trapped inside the flask of a sage with only the sheath. It was made from the wood of Bokusenō, given to his good friend, Inu no Taishō. An ancient yōkai tree, it was from Bokusenō that the sheath inherited its magical abilities, and this enabled it to contain the power of Tessaiga when Inuyasha sheathed the sword. In one episode this tree deity explained to Sesshōmaru the meaning of the two swords and what his father, the Great Dog Demon, intended. As Tenseiga's sheath was made from the same source, it boasted similar abilities. When Inuyasha first used the Wind Scar, Tenseiga formed a barrier and protected Sesshōmaru, which seemed to confirm this.


 * The sheath has occasionally been broken, but can be repaired, by leaving it beside a hive of yōkai bees, known as steel bees. Though it was not explained why they would, these bees will then use their beeswax to repair the sheath. These demon insects must be approached with extreme caution, as they are able to kill yōkai with their stingers. Once repaired with steel beeswax, the sheath will be as good as new, and its abilities will not be affected.

Trivia

 * In the English adaptations of InuYasha, Tessaiga was called Tetsusaiga (or Tetsaiga) due to an error in translation in the early days of the manga when the tiny っ (tsu) kana (which indicates a glottal stop, or a doubling of the consonant that follows it) was misread as a full-sized つ (tsu) kana, altering the romanization and pronunciation of the word. Both Tetsusaiga and Tessaiga can come from the kanji; the proper spelling depends on how the name is pronounced. The proper romanization is Tessaiga. By the time Viz, the company that translates the anime and manga, realized the error, it was too late.
 * Throughout the series, the Tessaiga's shape has changed between episodes. In some, it is curved near the end, and in others, its been completely straight (where it tends to somehow resemble a shape similar to one of the Buster Swords in the famous Final Fantasy series).
 * Though it was stated that any demon that touches the Tessaiga will get hurt, Shippō has been seen holding the Tessaiga once without feeling any pain, but it didn't transform. It is possible that it can also be held by those the Tesseiga trusts. Tōtōsai was also seen holding Tessaiga, and it even transformed, but it's possible that it transformed because he's the one who made it.
 * On another note, in Swords of an Honorable Ruler, Sesshōmaru briefly wielded the Tessaiga and it even transformed, but his hand was badly burned, when Inuyasha was possessed by the Sō'unga. Sesshōmaru also wielded Tessaiga in episode 134 to free Lady Sara from the demons that possessed her, and once again his palm suffered burns.
 * It was possible that the Tessaiga was, perhaps, sentient (for the reasons stated earlier). Other signs of proof include Sango stating (when Sesshōmaru was striking Tessaiga with his dragon arm) that it sounded like Tessaiga was crying. In the very same episode, when Tōtōsai struck the sword with his hammer, he claims it was singing a sad song. Some characters, like Sesshōmaru and Inuyasha, have been seen talking to Tessaiga directly.
 * The Tessaiga is available as a long sword weapon in the Monster Hunter 3 Tri, however it is exclusive to Japan.
 * Also available in Monster Hunter Portable 3rd only after clearing a download quest and obtaining tickets to create it.
 * Tite Kubo, author and creator of Bleach, stated that he based Zanpakutō off of the Tessaiga.
 * Tessaiga, along with Inuyasha, Shippō, Miroku, and Kagome make a cameo appearance in Ranma 1/2 OVA Episode 13. During one of Akane's nightmares, Tessaiga is seen in it's true form, stuck in the floor. Tessaiga is seen behind Inuyasha's and Shippō's dead bodies located on Akane's left.
 * Several of the Tessaiga's named techniques have a "crush" theme naming (with the kanji "破", meaning crush, rip, tear, or (more so) blast), nodding to Tessaiga's translation as the "Iron-Smashing Fang." (The "sai" and "ha" are two different kanji however.) The only exception is the Meidō Zangetsuha, which uses the kanji for "wave" instead of "crush."
 * In Episode 130: Shippō's New Technique, The Heart Scar!, a comedic filler episode, Inuyasha humorously told Shippō the real secret to using Tessaiga to its fullest was by making the right onomatopoeia noises when swinging it.
 * Technically, Meidō Zangetsuha was the first power Tessaiga ever absorbed.

Colmillo de Acero Tessaiga