Fencer Of Minerva

A relatively old softcore Hentai OVA released back in 1994 in Japan. It was one of Central Park Media's releases under the "Anime 18" label in 2001. A highly notable example of Porn with Plot with the "plot" half actually being decent, but it's also subjected to backlash from traditional and hentai fans for this reason.

The plot revolves around a pair of lovers resulting from a Childhood Friend Romance Gone Horribly Wrong named Diana and Sho; the former is a princess of the kingdom of Doria, while the latter is the rightful heir to the throne of the aforementioned kingdom, but lost that right when Diana's father, Randis, overthrew Sho's father, Baasen. The story opens during their childhood, when Sho proposes a bizarre Childhood Marriage Promise in that he hopes Diana would be his Sex Slave (as law in Doria allows women to be sold off as slaves for money) one day, much to her dismay. They are then attacked by several soldiers; one of them gives Sho a nasty facial scar, and he is ultimately pushed off a waterfall and presumed dead.

Twelve years later, Diana, now the princess of Doria, is set for an Arranged Marriage to Dunan of Guptia. She attempts to run away disguised as a boy, but is caught by a band of nomads and taken in as a sex slave. Before they can have their way with her, however, Sho, now living as a wanderer, happens to appear, and he takes her as his own slave. She happily accepts, and from there the two take on the political and personal turmoils set before them, all while enjoying each other's company.

Currently, it remains forgotten on the fence after Central Park Media's collapse. In addition to its backlash, it's known among a small, small circle for its borderline god-awful English dub. Interestingly, hero Sho is voiced by Crispin Freeman (who went under a pseudonym, naturally) in his only hentai role.

Tropes used in Fencer Of Minerva include:

The Ace: Sho
Action Girl: Takes her a while to get there, but Diana is actually a capable swordswoman, and actively helps Sho from the third episode on.
A-Cup Angst: Patris.
Anime Anatomy: Played straight, with the exception of female nipples. When video cassettes and DVDs of the show were first released stateside, Diana's nipples on the cover were erased.
Arranged Marriage: Diana and Dunan. It doesn't last long.
Attempted Rape: Good thing that Sho knows how to show up just in time, eh Diana? Sadly, the guy she's being forced to marry (Dunan) actually succeeds.
Bad Bad Acting: A major complaint from most reviewers is on the English dub, which is very wooden and forced. The voice actor for Sho (Crispin Freeman) has been pointed out to be the least offensive among them. Naturally, one can assume that the actors didn't really want to participate in a pornographic title...
Bratty Half-Pint: Patris, a rich young noblewoman who becomes smitten with Sho.
The Casanova: Sho.
Childhood Friend Romance: Diana and Sho.
Childhood Marriage Promise: More like a proposal into sexual slavery. They finally do get married in the fourth episode, but the slave-master relationship between Diana and Sho remains.
Crispin Freeman: Plays Sho, under the name Mark Percy.
Dark-Skinned Blond: Sho
Damsel in Distress: Diana in the first few episodes; the first by nomads (whose leader would eventually temporarily rule Doria) who subjugate her to humiliating "slave training" and whip her (Sho shows up and saves her in time); the second by Dunan who successfully rapes her (Sho finds her, and together they kill him); and the third by Patris and her bodyguard Kyle (Patris forces Kyle to molest her, but is interrupted by Sho. Later on, Patris' uncle tries to take Diana himself).
Dude Magnet: Diana, who becomes subjugated to a multitude of kidnapping attempts and rapes.
Everybody Has Lots of Sex
Good People Have Good Sex: There's something strangely warming about most of the scenes where Diana and Sho have sex. Diana is highly attractive, while Sho is a suave, handsome casanova who's also slightly perverted and experienced. They've been smitten with one another since childhood.
Hentai: Softcore, as in, there's plenty of nudity and action to go around, but there's no explicit depiction of genitalia, which makes this title stand out.
The Kingdom: Well averted, as the two kingdoms in focus (Doria and Guptia) have questionable morals. Doria allows women to be traded for sex and are treated as objects, while Guptia is a military-striving nation.
Ms. Fanservice: All of the female characters.
OVA: Five episodes, all of them around 45 minutes in length (which was the standard episode length at the time of its release in Japan).
Plucky Girl: Diana.
Porn with Plot *or* Plot With Porn: Very much depends on the viewer's interpretation. On one hand, there is a story with political intrigue and decent action (with equally decent animation): two childhood lovers find one another and try to survive freely while overcoming emotional challenges and the turmoils of two major kingdoms, and they happen to like having sex. On the other hand, sexual slavery drives the plot (and there is a lot of it), and there's some girl-on-girl action and S&M peppered in there. Diana gets molested Once an Episode and Sho isn't above polygamy.
Scars Are Forever: Sho has one on his face, and he covers it with a partial face mask. After he and Diana defeat Dunan, he gets rid of the mask for good, hence he seemingly overcomes this trope.
Sex Slave: A driving force of the story. In the end, Diana is monikered as queen of Doria's sex slaves, and she actually encourages women to take on slavery over freedom.
Smug Snake: Dunan.
Technicolor Eyes: Diana and Dunan have red eyes. It's easy to tell who's less morally questionable: Diana's eyes are a brighter shade, whereas Dunan's are a dark crimson.
Wandering the Earth; Sho lived like this for 12 years. He and Diana try to live together freely after Dunan and Diana's father are killed and Doria is relinquished to Sho, but ultimately must return when the replacement king, a nomad who befriends the pair, is nearly assassinated by the Guptians.
White-Haired Pretty Boy: Dunan.
You Gotta Have Blue Hair: Diana and several other characters.