Kuromaro(黒麿) is the fallen god who lives within Ontake Mountain. Kuromaro is responsible for the contract that nearly caused Tomoe's death over 500 years ago.
She was first suggested to be evil and malicious, having put the curse mark on Tomoe despite promising to turn him human and said to have a suffocating amount of miasma following him wherever he went. However, it is later shown that he may have kept his promise after all had it not been for a misunderstanding leading to Tomoe's inability to complete his own end of the deal.
In the Akura-ou arc, Ookuninushi's soul was sent to where Kuromaro is. She was shy towards Ookuninushi and said that she wanted to know what is love, and how to love. Ookuninushi offered to teach her what love is.
More than 500 years back, Tomoe had seeked him in an attempt to become human, fearing that he would outlive the woman he loved, who he believed was named Yukiji. However, for some reason he was unable to have spent the rest of his life with Yukiji, he gained the curse mark from which he would have slowly died from he had not met Mikage who suppressed the curse for the time being.
Though fallen from high respect, he retained his godly powers, giving him the ability to make a yokai a human. But, there were requirements, such as an item to represent the vow and the obligation to spend the rest of the individual's life with the special other mentioned. However should the individual fail to complete the obligation, a curse mark would be put upon him and due to having powers equal to those of god's, Mikage was unable to completely erase the curse mark from Tomoe and could only suppress it.
(To Tomoe) "This is the contract between us. On the next full moon, I will turn you into a human. However the condition is that you have to spend your entire life with that girl."
(To Tomoe) "I shall realize your dream. What is that Girl's name?"
(To Tomoe) " An outstanding demon like you is actually here in the mountains. What is your wish?"