Orion Heart: Injoku no Sukumizu Sailor Senshi

After defeating the demons, Orion Suns thought she could finally live in peace, enjoying her everyday life and love for Osamu, but she was wrong! The demons were still alive, and worse, their leader, Gildart, has now possessed the boy she loves, using his body to have their way with her! Who else will suffer as the demons run amok while she tries to save her beloved?!

(Source: OtakuStudy)