メディウサ

Medusa is a cruel and sadistic Dark Lord that's terrorized humanity for centuries. Originally born as a type of Gal Monster named Hebi-san, at some point during the Gele Era she encountered Demon King Gele and consumed her blood, resulting in her transformation into a Dark Lord.

On the year GI0815 Medusa formed a Demon Army and used it to invade the Magic Kingdom of Zeth that'd recently been formed on the southwest of the human territories, bordering with the Forest of Monsters of the Monster Realm. This year came to be known as the "Medusa Dark", and her name became immensely feared among the citizens. The year she spent savaging the land was so savagely brutal that it encouraged the mages of Zeth to build a defensive barrier named the Mazeel Line to prevent more invasions from Dark Lords. Not satisfied, 32 years later she performed a 2nd invasion but the defensive system built pushed her back, preventing a second Medusa Dark.

During the division of the Monster Realm that took place after the death of Demon King Gi, Medusa decided to join the Kayblis Faction, targeting Kurusu Miki to take her life so that Kayblis can become the new Demon King instead. The following years the Kayblis Faction and the Hornet Faction have been in a state of total war. Most of the times she doesn't join the fights and when she does she makes her goal to capture a female Dark Lord from the opposing faction to be able to toy with her, but so far she has failed in capturing any.

(From AliceSoft Wiki)