Hiraikotsu

is Sango's gigantic boomerang and her primary weapon. Like the rest of the arms and armor of the people in her village, it was made from parts of vanquished demons. In Hiraikotsu's case, it was made from purified demon bones. Because of its supernatural material, it's nearly unbreakable and is a very powerful weapon. It appears to be stronger than steel, while having a tremendous weight. It was destroyed in episode 12 of InuYasha: The Final Act, chapter 485 in the manga, but was repaired by Yakurōdokusen, and was imbued with a new type of power that has the ability to destroy demonic energy like Tessaiga's Bakuryūha.

Sango uses Hiraikotsu in many different ways. The leather bands at either end allow her to grasp and handle it easily. At six feet in length and what must be fifty pounds or so, she handles Hiraikotsu very nimbly. Miroku states in the first movie that she must be very strong in order to be able to lift and carry it. Other than using it as a boomerang, she can swing it and wield it as a melee weapon. She's killed countless demons in this way, as well as hitting Miroku over the head when he was acting as a pervert around women. Hiraikotsu is also big enough for Sango to use it as a shield when the need arises, and the nature of its material makes it excellent for that purpose. When not in use, she uses a strap, possibly made of leather, anchored on either end by a buckle and using friction to hold the strap ends in place. She slings the strap over her right shoulder and the strap crosses down her body to below her left hip.

Sango has the basic knowledge and experience to repair Hiraikotsu; she likely was required to learn how to do so, as she sometimes went on exterminations alone. In the anime she had to return to her village to repair a large crack in the surface. The demon bones are worked as if the material was steel. A blacksmith's furnace is used to heat the weapon and bones until red-hot, and more bone is used to fill the crack, repeatedly struck with a blacksmith's hammer. According to Sango's comments, it was likely her father that taught her how to do so. While she admits that her father's handiwork would have been better, she was able to perform repairs of a quality that she was more than happy with.

Although Sango is very attached to Hiraikotsu, she is not beyond sacrificing it to save those she loves. In Inuyasha the Final Act, while trapped by a dangerous bone-collecting demon, Sango destroys her valued weapon with poison to save Miroku and herself from being devoured. Sango and her comrades are led by Myōga to a mysterious demon potions maker whom Myōga claims can revive Hiraikotsu.

The Potions Maker agrees to fix it, dissolving Hiraikotsu in one jug and telling Sango to slay the demons in the second jug, warning her if she failed Hiraikotsu would dissolve into nothing. Sango then is determined to reclaim her weapon and jumps into the jug, and is quickly confronted by multiple demons. While trying to fight them, the demons angrily demand why Sango sacrificed them. Sango realizes the demons she's facing are what created Hiraikotsu. Hiraikotsu is furious Sango would sacrifice it for a human man, Miroku, and demands that Sango never betray it again and abandon Miroku. Sango refuses, declaring if Miroku died she wouldn't be able to live, thus, she would sacrifice Hiraikotsu again to save him. Hiraikotsu is further enraged and decides to kill Sango, however, it senses Miroku's resolve to protect Sango at the cost of his life and changes its mind. Hiraikotsu then admits it cannot understand human love but Miroku's courage has impressed it so it revives as Hiraikotsu to fight by Sango once more.

After Hiraikotsu is reforged, it gains the power to absorb poison and disperse it, making it much more dangerous against Naraku and enemies.

Name

 * Hiraikotsu's name is made up of 3 kanji (飛来骨). A kanji is a form of Japanese writing that each mean a different word by themselves, and can be combined to make new words; the first Kanji, pronounced with "Hi" in this case, means "Flight" or "Flying". The second Kanji, pronounced "Rai" in this case, means "to come" or "to return". Considering it's basically a giant Boomerang, the "Hirai" part is a way of saying in pure Japanese that it is a weapon that flies back to you. Finally, the last Kanji, pronounced "Kotsu" in this case, means "Bone", referring to that it's made from the bones of demons, and thus is basically one big bone. The name itself has been interpreted many different ways, but considering it's kanji and function, the term "Flying Return Bone", or possibly "Bone-a-rang", is likely the most correct translation.

Trivia

 * As stated by Miroku in InuYasha the Movie: Affections Touching Across Time, the Hiraikotsu is much heavier than it appears. Sango is able to wield it with ease, making it appear as though it's lighter.
 * It is possible that the Hiraikotsu could be based from Ukyo's Giant Spatula from Ranma 1/2, which is another series made by Rumiko Takahashi . Not to mention that both users of each weapon are voiced by the same person.
 * In the anime, it was cut in half at least twice, but in the following episodes, it was showed to be intact without explanation. In episode 56, it only had a crack. However, in the next episode, Sango had to repair it. In the manga when Kaijinbō cut it in half, Tōtōsai was shown to be the one to repair it. As such, it can be assumed that the same thing was done during or after episode 45 off screen.

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