Watching Mnemosyne was kind of like watching softcore porn on Cinemax with blood, gore and torture tossed into the mix. However, the plot to Mnemosyne wasn't entirely an excuse for gore and sex as there was a decently put together plot to pay attention to throughout what some have mistakenly believed to be an OAV as this was actually made to celebrate the Japanese AT-X network's 10th anniversary by airing the series monthly on the channel. You will notice as episodes progress that Mnemosyne tends to do several time jumps in each of its first five episodes starting from the early 1990s (the era where 128 MB of RAM at the time was plenty of computer memory) and eventually in the middle of the 21st century (where it's possible to download things into a physical form). In each episode, Rin and Mimi get caught up in an incident involving a member of the Maeno family and/or involving one's search for immortality which is somehow connected to the Yggdrasil tree fruit that give Rin and Mimi their immortality. What may seem to be a confusing style of storytelling with Rin and Mimi introduced to a new descendant of the Maeno family for three generations does eventually makes enough sense by the time the fifth episode rolls around, especially if you pay attention to some small scenes in the first four episodes that culminate to something bigger in the final two episodes. Events with the series do end decently enough with a decent amount of depth given to Rin, Mimi and the Maeno family as they interacted with one another. Visuals to the series were decent with use of faded colors to blend with the dark feel of the series with a decent amount of detail for both scenery and character designs. Animation was also decent at some points (some action scenes) and non-existent in others (still shots with minimum animation, especially in some of the show's sex scenes).
Still, this is a show with enough graphic violence and sexual content that is near hentai levels which definitely shouldn't be shown to younger viewers nor first-time anime viewers for that matter. With the show used to celebrate AT-X's 10th anniversary, it's quite clear the show was doing all it could to push the envelope with violence and sex and it definitely shows considering the many gory ways that immortal women are killed or tortured and the various sexual scenes portrayed like orgies, oral sex and sadomasochism. Another problem I did find was that the antagonists tended to be a bit on the shallow side compared to the protagonists and the Maeno family where villains liked Apos and Laura lacked the depth that Rin and Mimi were given.
For a heavily violent and sexual title, Mnemosyne has decent plotting and character depth involving the passing of decades as Rin and Mimi are involved with the Maeno family and dealing with Apos. But the heavy use of violent and sexual content won't make this a title that all folks would want to see.