Tessaiga

was a sword wielded by the hanyō Inuyasha. It is the opposite of Sesshōmaru's inherited sword, the Tenseiga. Out of the two, Tessaiga is "the sword of destruction", while Tenseiga is "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. And the same goes for Sesshōmaru's Tenseiga.

History
The swordsmith Tōtōsai created the Tessaiga from a fang of the daiyōkai the Great Dog Demon, the father of Inuyasha and Sesshomaru. In its 'docile' form, the sword looks like a regular (and rather battered) katana. When wielded properly, it transforms into a weapon roughly the size of a car bumper that somewhat resembles a falchion. The Tessaiga will only transform if the user cares for humans and has yōki, this means that humans can never wield it because they do not possess yōki. The Tessaiga has the power to slay 100 demons in one swing by striking the Kaze no Kizu, it also has the ability to absorb the technique or skill of a strong yokai that is defeated with the sword.

The Inu no Taishō used the Tessaiga to steal Shishinki's Meidou Zangetsuha technique, but because of the danger the technique bore the Tenseiga was created to contain it. When the Inu no Taishou died a barrier was put on Tessaiga to prevent full yokai 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. Sesshomaru 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 is unable to touch the sword, Inuyasha is not only able to wield it, but uses it to defeat Sesshōmaru. After the battle Inuyasha becomes the master of Tessaiga and begins to use it to aid him in battle. During a battle with the Thunder Brothers it's revealed 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 Sesshomaru (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 shown the power by summoning 100 demons and slay 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 is 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 keeps 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 becomes much sharper and sturdier, able to match a sword forged from the tusk of Goshiniki, the same Oni that originally shattered the sword. After much training, Inuyasha learns how to use a greater power based from that of the Kaze no Kizu to take out a powerful enemy, that is known as Bakuryūha.

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

Gaining New Powers & Ablities
As Naraku becomes stronger, Inuyasha begins to use Tessaiga's useful power/ability-absorbing ability to strengthen the sword with new-much, 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 Tetsaiga gained the power and ability to break through barriers.

Subsequently Tessaiga absorbed Hōsenki's Kongosha 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 Hosenki and strengthen the sword. Kongosoha 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 yoki 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 yoki it nearly took all of the Tessaiga's powers, but Inuyasha used his sword to destroy Dakki and gained the ability to absorb yoki in the form of Dragon Scaled Tessaiga. Inuyasha didn't master the Dragon Scaled Tessaiga right away unlike the previously acquired powers. Being a hanyo limited the amount of yoki Tessaiga could absorb before the yoki 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 yoketsu 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 allows the user to send their enemy directly to Hell. In the final battle with Naraku, Inuyasha fully masters the technique and it changes into an attack that cuts an enemy and then send the remains directly to Hell itself.

General appearance
At first glance when not in use, the Tessaiga appears 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 turns into an over-sized dog's fang, fitting for its name. The cross guard turns into a large patch of fur similar to a dog's also. In the later chapters and episodes, the blade not only becomes slightly larger, but changes colors and transforms according to the abilities it absorbs.

Katana Form

 * Anti-demon barrier: Inuyasha and Sesshōmaru's father put a protective barrier within the sword, so that any pure demons whose intent are to harm humans will be rejected by the sword and not allowed to touch it. The sword can be wielded by demons, if it has a good heart towards humans or has something to protect. Shippō, a full demon who does not feel the urge to harm and willing to help humans, is able to hold the Tessaiga without feeling any pain. Inuyasha, being a half-human half-demon, can wield the sword fine, though he can only activate it once he desires to protect humans. As a powerful demon, Sesshomaru can wield the sword for a short period of time. Humans can wield the Tessaiga in its untransformed katana state.
 * Human Shield: The Tessaiga protects the human that is holding it.

True Form

 * Kenatsu: (lit. Sword Pressure, 剣圧) is the special ability that allows the Tessaiga to cut opponents without touching them surrounding the blade in yōki. Inuyasha uses the ability before he learns the Kaze no Kizu.
 * Kaze no Kizu (lit. Scar of the Wind, 風の傷) Wind Scar in the English dub: Special attack that kills 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 is gained by sensing the fissure or scar between 2 demonic forces. After his battle with Ryukotsusei, Inuyasha learned to put his own power into the attack so the fissure appeared around Tessaiga's blade and could be triggered instantaneously. Until he gained that ability, it was not very useful against Kagura since she can change the demonic winds.


 * Bakuryūha (lit. Bursting Stream Blast, 爆流破) - Backlash Wave in the English dub: Tessaiga's ougi (or ultimate technique). Uses the opponent's strong demonic forces and unleashing the Wind Scar at the right point, the demon's energy will be reflected back with the added power of the Wind Scar. Power is amplified many folds. Gained by Inuyasha defeating Ryukotsusei and reflecting his power back at him. However, two requirements are needed in order to implement the Backlash Wave. The first is that Inuyasha can only reflect pure energy attacks. The second is that his own demonic aura must be much stronger than his opponent's or the Backlash Wave will not form. It is seen in the Inuyasha movies (though never in the series proper) 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 shatters barriers (including Naraku's for a while). When used, Tessaiga glows red. Only the strongest barriers cannot be shattered by this attack such as Naraku's. Since gaining the effects of Shiori's orb, the blade turns red when a barrier is cut.



Diamond Tessaiga

 * Kongosoha (lit. Diamond Spear Blast, 金剛槍破) - 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 are able to pierce Naraku's stronger barriers. Inuyasha is also capable of combining this technique with his Wind Scar.



Dragon-scaled Tessaiga

 * Yoki Absorption: Having defeated Dakki, Tessaiga gains the ability to absorb a opponent's yōki directly. Inuyasha, being a hanyō, limits the amount of yōki the sword can absorb before regurgitating it back on the user, until Tessaiga absorbs senki which purifies the yōki and stopping the regurgitation.
 * Yoketsu Cutting: After realizing the true nature of the Tessaiga is to cut Inuyasha learns to see yoketsu and uses the Dragon Scale Tessaiga to cut it, instantly destroying a normal yōkai, beings created of many different yōkai like Naraku and Moryomaru have several yoketsu and cutting them will destroy parts of their body and prevent regeneration of the same. It can also cut the large amount of yōki emitting from a strong yōkai, which can be fatal.



Black Tessaiga

 * Meidō Zangetsuha (lit."Dark Path Slashing Moon Wave, 冥道斬月波) This technique was attained when Sesshōmaru's Tenseiga broke on to Tessaiga. The original technique creates a path to hell by creating a giant circle that can suck anyone in it's path, though it can also be used to escape from a Meido one is already in, as well as entering/exiting pocket dimensions as was seen at the end of Inuyasha and Sesshōmaru's final battle for Tessaiga, as well as being the method that Shippō and Kohaku used to enter Naraku's final form.
 * Cutting Meidō Zangetsuha: When Inuyasha completely masters the Black Tessaiga the Meidō Zangetsuha changes to symbolize the Tessaiga's true nature, a sword that cuts. The new Meidō Zangetsuha can 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 adding the Tetsaiga's cutting nature. It seems to be stronger than the regular Meidō, as it was able to tear apart Naraku's final form, which was impervious to the original technique. Inuyasha has also used it as a method of crossing through to Kagome's time for the final battle, and even into the Shikon no Tama itself.

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 is capable of resisting any amount of offensive force; however, if that force is used continuously then the sheath will crack. This 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, the sheath inherits its magical abilities from him, and this enables it to contain the power of Tessaiga when Inuyasha sheaths the sword. In one episode this tree deity explains to Sesshōmaru the meaning of the two swords and what his father, the Great Dog Demon Inu no Taishō intended. As Tenseiga's sheath was made from the same source, it boasts similar abilities. When Inuyasha first uses the Wind Scar, Tenseiga forms a barrier and protects Sesshōmaru, which seems 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 is 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 is 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 touch 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 its 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 is possible that the Tessaiga is, perhaps, sentient. As 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.
 * 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, Tetsaiga is seen in it's true form, stuck in the floor. Tetsaiga 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", which 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."