@RexNemorensis Kiyohime is a figure from a folktale about a woman who fell in love with a traveling priest. She is framed as either the daughter or widow of a landlord, whose property was used to house and entertain traveling priests on their pilgrimages to the temples in the region. She fell in love with a handsome priest named Anchin, but over time he lost his own passions for her. In rage from the rejection and his attempt to bail on her, Kiyohime pursues him and transforms into a snake creature. Anchin escaped to Dojijo temple and hid under one of its bells, but Kiyohime tracked him there by scent. After coiling around the bell, she clanged it a few times with her tail before breathing fire over the bell, melting it and killing Anchin. All these points in the folktale are things Bunbuku here replicates in his little transformation battle in these last pages and the first few pages of the next chapter.
Though I am sure more of the reactions to the transformation is because of Fate/Grand Order, where Kiyohime is one of the characters in that.