The original is an 8-volume light novel series from the 1980's (6 are legally available in English, last 2 coming this year/next year), two 1-hour OV As
from the 90s that apparently has a slightly different plot (not legally available in English but there are fansubs) and a new OVA series of 4 half-hour episodes that either just came out or is just about to come out (also not legally available in English but I expect that fansubs will shortly follow).
I've only read the first few volumes of the novels, and while there is explicit, kinky sex (BDSM is involved, and sex slavery is a plot point), there isn't very much of it; one scene each in V1 and 2 and two in V3 (the translated volumes are around 175-200 pages of prose each, so they're a bit shorter than a standard US novel, but there's still a pretty high story/sex ratio). I have only seen clips of the 90s OVA, none of which included any sex, so I can't report about that, or on the new OV As
Mostly the 3 volumes I read focus on dystopian sci-fi; the society has a rigid caste system, one character (Riki) is a non-citizen slum-dweller of the lowest social class and the other (Iason) is a high-ranking artificial human (cyborg? it's unclear) of the highest social class. There's interminable infodumping about the society and technology, long side plots about gang wars, black market racketeering, genetically engineered human "pets", etc. I don't know if it gets pornier in the later volumes; I have the six that are out and can try to polish the rest of them off later this week / weekend and report back.
The one thing so far that is worth reporting is that the first sexual encounter between the characters happens (in flashback, in V2) when Rikki is 16-ish (Iason is artificial but apparently looks 20ish?); Riki, a street gang leader and small-time hoodlum, is caught pickpocketing (which, as he's a non-citizen, is close to a death sentence), Iason refuses to press charges (for no reason), Riki feels indebted and offers to pay him back with sex, Iason accepts but is snarky about it and Riki comes out pissed off and hating Iason. The scene is fairly explicit but focuses mainly on Riki being annoyed and humiliated by Iason's arrogance and disdain.
Then some time later (the series isn't terribly clear on the chronology) Riki, who is doing interplanetary drug/slave-running, stumbles into some sort of shady deal that Iason is involved with; Iason takes him prisoner and uses him as a sex slave for a year or so (resulting in the other 3 sex scenes so far), then lets him go (this is all extended flashback, mainly V2/V3). The main plot kicks in after Riki returns to the slums (at which point he's 19) and re-forms his gang; the story then gets into an ongoing conflict with another gang plus internal politicking in Riki's gang (some of the new guys resent his return and want to depose him). That's where I stopped reading (I was going to wait for all the volumes to come out, because I was already getting lost with the various secondary characters reading them every six months as they came out).