Mu-onna
In Japanese folklore a Mu-onna (無女 lit."nothing woman") is a type of yōkai, a supernatural monster. A Mu-onna is a vengeful spirit of a mother who lost her child to famine or war. She protects children in danger, but may also try to merge or absorb them. They can look into the child's soul to find information while merging with them.
To gather the information, or to merge with them, the Mu-onna must cast a spell to put the child's soul to sleep.
Since the Mu-onna is made from a mother's tender feelings, she may be willing to allow herself to be destroyed for the sake of the child.
In popular culture
In the Anime/Manga series Inuyasha, Mu-onna (also known as the "Un-Mother" in the English dubbing in the anime) made a debut in the anime in episode 5 and Chapter 13 in the manga. She was a demon that on Jaken's orders tried to get information on where Inu no Taisho's tomb was located, after this failed she tried to completely absorb Inuyasha before she was destroyed by Sesshoumaru's claws, sacrificing herself by using her body to shield Inuyasha from his half-brother's attack.