Rance

Rance is a long running series of erotic RPG and SRPG games developed by Alicesoft. Obstinantly the protagonist Rance's goal is to sleep with every woman in the world, but achieving that often requires him to save the world as well, leading to him forming parties of heroes, leading massive armies, or training squads of monsters.

One of the Rance offshoots is Rance Quest: Monster Girls, but the name is slightly a misnomer. Instead of being about monsters who are girls, it's about girls who are monsters.

Kamilla
Kamilla is one of the leaders of the Monster Realm in Kichikuou Rance. In addition to being a demon she is also half-dragon. After being made a Dark Lord her dragon armies decimated those of the demons and brought peace to the realm. Unfortunately this also angered the god of the Monster Realm, who wiped out the dragons in response. In Rance 6 she led an army of monsters successfully agaisnt Zeth, but could not defeat Rance and was locked away in a dungeon.

Medusa
Medusa is a former human who was made into a Dark Lord due to her savgery and depravity. In addition to her immense physical strength she also has a phallic albino serpent attached to her body that she enjoys eating girls with.

Noir
Noir is one of Masamune's Youkai wives in Sengoku Rance.

Omachi
Omachi is one of Masamune's Youkai wives in Sengoku Rance, and former leader of the Youkai forced in the Great Youkai War. After being defeated by Masamune she fell in love with him.

Tamagushi Fuuka/Orochi
Fuuka is an amnesiac miko traveling through Japan. She can be recruited to Rance's army in Sengoku Rance. After Rance hears about the Orochi, and the sacrifices of women that must be made to keep it sated, he decides to kill it and put an end to the sacrifices. After surviving through the dungeons of the Miko Institute, filled with the msot powerful opponents in the game, it is revealed that Fuuka is actually the Orochi herself. She convinces Rance to kill her so that her soul can rest.