Ryūjin

was a demon who commanded Toshu the human swordsmith to create a sword for him and was later killed by him, following the blade's completion.

He first appeared in manga chapter 386, where he killed a couple of villagers while searching for Toshu but then was quickly chased off by Inuyasha. Toshu claimed that he met Ryujin a year ago while travelling through the remains of a battlefield, and that Ryujin demanded that Toshu forge a sword for him using his scales. It was later revealed that it was, in fact, Toshu who'd offered to make the sword for Ryujin, as Toshu wanted to use Ryujin's scales to make his sword the strongest in the world. To ensure that Toshu complied with his demands, Ryujin marked Toshu's eye.

He appeared again after Inuyasha's group decided to protect Toshu, and managed to repel Inuyasha's Wind Scar attack with his shield. His success lay in the fact that his shield was also made out of his scales, thus enabling it with the power to absorb youkai energy. His weakness, however, was that parts of his body lacked scales, as he'd ripped them out to forge his weapons. Inuyasha breaks his shield and injured him heavily, making it easy for Toshu to kill him.