Meiōjū

is a demon that possess an impenetrable shell that has taken blows from Inuyasha's Kongōsōha yet it didn't suffer any damage. Meiōjū was absorbed by Mōryōmaru, who desired the demon's impervious shell as a defense against his enemies, especially Naraku.

The only attack known to have been able to breach this shell was Sesshōmaru's Dragon Strike, though his sword broke as a result. Meioju has a powerful attack; Raimeihō (雷冥砲) which are spheres of black lightning.

Coincidentally, his seiyū, Tadahisa Saizen, also voices Gōra, who is also a turtle demon.

Manga VS Anime
In the manga, Meioju after being brought back to life by a piece of meat Moryomaru, assaulted a village in which it is housed his impenetrable armor. After several attempts, and with the help of Byakuya, he manages to reabsorb the armor, and collect the Kongosoha of Inuyasha. Being controlled by the fragment of Moryomaru is absorbed by it.

In the anime, he simply just revived and regenerated, and is immediately devoured by Moryomaru in a quick scene. Furthermore Moryomaru demonstrates to be able use the Raimeihō of Meioju (having devoured), against Sesshomaru and Koga. However, in the anime this technique has never been seen to be used by Meioju, because never seen him fight.