It's hard to draw a hard boundary line around hentai sometimes. Any anime fan from 2010 can attest to the fact that Yosuga no Sora made plenty of waves for being the pinnacle of the practice of making anime “for the plot”, but it's hard to watch full-on sex scenes shot from a slightly obscured angle and imagine they really were playing to the spirit of hentai labeling laws rather than the letter. By contrast the 1997 manga Futari Ecchi is routinely labeled as hentai, featuring not only sex scenes in every chapter, but taking perhaps the most explicit angles possible, even shots from within people's bodies.
This seems like an easy one to label, but the point of Futari Ecchi isn't primarily to titillate readers (although it does, in spades) so much as it is education. Following the newlyweds Yura and Makoto from their staggeringly awkward first nights to eventually realizing a fully fledged and even somewhat experimental sex life, every step of the way is filled with cutout blurbs about safety, pleasure, anatomy, and even national statistics. Manga as instruction isn't unprecedented, but to maintain a story for over 20 years of serialization with widespread acclaim and recognition all the while is no small feat for porn.
Five years after it began publication, Futari Ecchi received a two-season OVA adaptation for the first few chapters. But besides the name, it would be hard for someone casually stumbling across the series online to suspect that it was originally instructional hentai, from the R+ rating instead of X—avoiding the hentai label with exactly the same camera tricks as Yosuga no Sora —to credits like Chiaki Konaka (who scripted, among other cult classics, the equally suggestively named The Big O ) and Project A-Ko 's Yuji Moriyama. That and the fact that far away from having advice to sex seekers, there's very little in the way of teaching in the OVA, or at the very least, as little teaching as an adaptation could have.
This leads to a number of unfortunate issues. Between the first and second episodes of the first OVA, we transition from Yura and Makoto feeling nothing but nervousness to suddenly being vigorous thrill-seekers, having sex in odd places at opportune moments. The image of Makoto as dopey but earnest, and of Yura as easily embarrassed but kind and gentle, reminds us that even the most innocent couples do enjoy a healthy and often voracious sex life. But after that point their understandings and discoveries plateau, and we're left with the same sex in slightly different locales, much more akin to a run-of-the-mill hentai than fans of the manga would expect from Futari Ecchi.
It's also much more difficult to see anything subversive in the anime adaptation. Soft-spoken Yura's enjoyment of sex aside, she seems to mostly play a passive role in their sexual encounters, and even frets about not pleasing Makoto when really he's the only one climaxing most nights. The arc resolves with her learning how to give oral sex, and after succeeding they proceed right back to regular vaginal sex, with a throwaway line about him lasting longer having already come once. Seems hardly like a cause for celebration of Yura's triumph of the will. Likewise Yura's sister Rika is young but promiscuous, with an assertive personality and tons of boyfriends at her call. While she provides a great counterpoint to Yura as someone in control of her own sexuality, virtually all her sex scenes also put her at the mercy of her sex-crazed male partners. One could argue she's just submissive, but it seems a bit too much to put her and Yura in the same role, and at some point it's easier to assume they just went with the gender roles everyone would expect.
Futari Ecchi 's core is in transmitting the same realistic image of married life that the manga had, with the time commitments of a job set against the gentler romantic moments together played well. Once again we see it very much a product of an earlier time, with Yura devoting herself to household work while Makoto works long hours as a salaryman. In the last episode Yura gets a part time job as a waitress, and the potential sexual harassment it entails for her. While thankfully Makoto turns out to have nothing against his wife also working, he does feel jealous of the other men looking at her, leading her to quit at the end of the episode. It's a hodgepodge of questionable statements on trust, permission, and Yura's role in the household, and looking back on earlier episodes their married life has a similar sort of tint. Considering how these elements could have been balanced or expanded on, the Futari Ecchi OVA is really kind of a shame.