I'm going to mention what all I remember. I can remember the start of the plot pretty well, but I can't remember anything specific enough that search results can pull up. The start of the manga was set back during the time of the samurai. It started with two men finding a house in a forest with a beautiful women living in it. She allows them to stay in her house as long as they do not enter the back room. After a while one of the men falls in love with her and they begin a relationship, but the man's curiosity gets the best of him and he looks into the back room. I can't remember exactly what he saw, but I know shortly after that he figures out she is immortal. He chooses to stay with her and she agrees to make him immortal as well. Before anything happens they are attacked by people hunting her to figure out the secrets of he immortality. The man defeats all of them but is fatally wounded in the process, so the women makes him immortal. However almost immediately afterwards he friend from the start shows up a decapitates him. The next thing I remember is him waking up like 100 years later all bandaged up in a new era, and that's as far as I remember. All this may not be 100% accurate, but it's been a while since I found it, and I can't remember why I didn't finish it. Any help would be appreciated

Kurozuka I think

That's the one I was looking for. Thank you

Yeah, sounds just like Kurozuka.

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Is this me in a nutshell?
Pretty much.