孤高騎士メリッサ～反逆女騎士異種姦陥落～

The royal capital is occupied by magical forces when the royal forces are absent. Royal Guard Melissa, in reaction to the princess and her subjects being taken hostage, tries to assassinate the ringleader while acting as a sex slave, but fails.

For her betrayal, a ghastly hell of rape awaits. As her body is tampered with, her sprit crumbles while the demons feast on her...

[From MangaGamer]