I've been trying to find this manga. The mc gets isekaied to a demon forest and somehow makes it out. He then meets a female knight that he can't understand, because they don't speak the same language, so she takes him to a nun/priestess who casts a spell that lets him understand them. I think I remember him claiming to have amnesia to cover his back story. The nun/priests takes care of him until they think he's ready and capable on surviving on his own. Then eventually the nun/priestess gets charmed/hypnotized and taken by a demon/vampire/Incubus impersonating a noble/mayor/aristocrat. So the mc goes to save her and ends up fighting and defeated him with the female knight from the beginning of the story's help. The female knight is injuried or poisoned to where she goes into extreme heat(horny). The mc has sex with her to save her. I think I remember there being a special or powerful sword not sure if it was involved in saving the female knight. The nun I believe is unable to be saved and dies. The mc and the female knight team up for now and continue on a journey.
Not too sure but I think that the mc was special in a certain way when he was taught magic by the nun in the beginning. He might have been able to use all types of magic or something and kept it a secret considering it was abnormal for people in that world.
That's about as much as I remember from the manga.