Elf ni Inmon wo Tsukeru Hon The Animation

Sylpha, a guardian of the forest, fights and is defeated by a mysterious man who attacks an elven village and steals its treasure. Humiliated and with a lewd crest on her abdomen, her body is consumed by pleasure every day. She sets off on her own, determined to lift the crest while she can still retain her sanity and recover the village's treasure. However, Sylpha's body continues to be at the mercy of the pleasure of the crest.... What will be Sylpha's fate?

(Source: showten, translated)