From an older anime called Yaiba. IT is episode 49. A character names Kaguya possessed one of the heroines for much of the season and finally transforms into a giant "thing" after absorbing enough essence.
I'd upload it to my channel, but well, I made a post about that some time ago, so just use the link. Must have a Facebook account to view the contents. It is at the beginning of the episode.
https://www.facebook.com/yaiba24to52...0326427891243/