Ryūkotsusei

Ryūkotsusei (竜骨精, りゅうこつせい, "Dragon Bone Spirit") is a giant dragon daiyōkai in the manga and anime series, "InuYasha".

InuYasha's father first fought him in the older days and sealed him away with one of his claws. As it is mentioned in one episode, they say that Inu no Taishou mainly died from the wounds he received from Ryukotsusei. Following Tōtōsai's explanation, InuYasha stubbornly went to fight Ryūkotsusei so that his sword would become lighter and easier to use again. Myōga tells InuYasha that since the dragon is already sealed, all he must do is stab the dragon in the heart to kill the dragon and "surpass his father". However, InuYasha complains that this is not his style and would prefer to fight the dragon head on. InuYasha has his wish fulfilled when Naraku removes his father's seal so that the dragon would awaken to destroy InuYasha.

's wind tunnel was unable to absorb the attack and only slightly changed its trajectory away from InuYasha. Ryūkotsusei is ruthless and has a mask that exists on his forehead through which he speaks . His attack is Raigekidan (Thunder Attack Bullet), which is the form of a giant white ball of explosive energy, which he emits from his dragon mouth instead of fire, and could easily have defeated InuYasha with a final blow if InuYasha wasn't able to learn and use the Bakuryūha (Explosive Flowing Wave) just in time to defeat the dragon. Myōga's protests reveal that it was Ryūkotsusei who inflicted the severe injuries on InuYasha's father that were the main cause of his death shortly after sealing Ryūkotsusei away. In the , he survived long enough to save Izayoi and their newborn child InuYasha. He was still weak from his battle with Ryūkotsusei, but put protecting the laboring Izayoi above all else and recklessly rushed into battle, which caused his demise. It is strongly implied in both the manga and the anime that there were other equally powerful demons also fighting InuYasha's father, and it seems that Ryukotsusei was the only one who managed to survive the fight with him.

Since he is a daiyōkai (great demon) with red eyes and silver hair similar to Inu no Taishou, Sesshomaru, and InuYasha, it is speculated that he may have a human form as well. This is because all the other daiyōkai in the series, such as Inu no Taishou, Sesshomaru, and Hyoga, seem to have both human and demonic forms. However, it is unlikely we would ever find out.

Ryūkotsusei is seen in the second ending, "Fukai Mori" (Deep Forest), where Sesshomaru visits where he was sealed.

He is voiced by Kazuhiko Inoue in the Japanese version and in the English dub by Trevor Devall.