Human who loved Midoriko

The is a manga only character.

History
He was a man who secretly loved the ancient priestess Midoriko hundreds of years before the events of the series, during the Heian Period of Japan.

Many minor yōkai (dragons, ground-spiders, oni, etc) possessed this mortal man who desired Midoriko and formed into one yōkai in order to kill her, similar to how Onigumo loved Kikyō and created Naraku.

However, rather then an hanyo like Naraku, the resulting creature was a full yōkai, completely devoid of human feelings. While Onigumo's body was completely devoured by demons and his evil spirit used as their adhesive, the human who loved Midoriko was killed and forcibly absorbed on the base of the dragon's neck, where the head and right hand of his corpse are visible, of course not inside the jewel since there are only the yōkai's spirits.

Personality
Nothing is known about his personality outside of that he privately yearned for Midoriko and that this hidden impurity allowed the yōkai to possess him. In the illustration accompanying Sango's story, the man is huddling in fear as the yōkai converge on him, which could imply that the possession was against his will.

Physical description
Much like Midoriko in the manga, his features are kept hidden in flashbacks and only his mummified corpse is seen.

Midoriko
Not much is known about Midoriko and the human's relationship, if they even had one, other than the fact that the human was secretly in love with Midoriko.

Trivia

 * In episode 25 of The Final Act, we can see a face on the demon's neck resembling a mask, similar to Ryūkotsusei's face.