I can't give any examples really as I haven't read much in the way of hard sci-fi manga. Closest I can think of is Gokukoku no Brynhildr. I'm looking for stuff more mature or "darker" in concept than that, however.

Really any sci-fi is fine, from mecha, aliens, evil labs, etc as long as they have a dark concept and either ecchi or mature tags. I could just search under those tags, but I'm not sure what's good, so I'm hoping fans of that particular type of manga could point some out.

Thanks!

In a world where troubled young hearts are besieged by evil spirits, only one can wield love as a weapon: the God of Conquests, Keima Katsuragi.

Kamiyadori comes to my mind.

Oh ho! Nice. That'll do, sir, that'll do. 😀

I love that picture on MU's page for that title. She's looks pretty fierce.

In a world where troubled young hearts are besieged by evil spirits, only one can wield love as a weapon: the God of Conquests, Keima Katsuragi.

Did a search for you, sci-fi/ecchi and dark ambience tag. Found the manga you mentioned and this Blame Gakuen! and So On. Seems to be a series of oneshots though?

"The oldest and strongest emotion of mankind is fear, and the oldest and strongest kind of fear is fear of the unknown"

Try Freezing, it should fit most of those areas.

You should try Hagane as well.

"Thus is our treaty written, thus is agreement made
Thought is the arrow of time, memory never fades
What was asked is given, the price is paid"

Quote from EternalNightmare

Did a search for you, sci-fi/ecchi and dark ambience tag. Found the manga you mentioned and this Blame Gakuen! and So On. Seems to be a series of oneshots though?

Thanks. I would do the same, but would rather get actual recommendations rather than a list of everything carrying the tag, that's all.

I'll check those out anyway though! Can't hurt to try. 😛

Quote from halohero

Try Freezing, it should fit most of those areas.

I've heard of that manga before a few times. Very ecchi. I read the first few chapters, and it looks promising.

Quote from Draconic

You should try Hagane as well.

I gave this one a try too. It's pretty good, nice dialogue and the main heroine is cute. I look forward to seeing where this one goes.

In a world where troubled young hearts are besieged by evil spirits, only one can wield love as a weapon: the God of Conquests, Keima Katsuragi.

Eden (ENDO Hiroki)?

Not really ecchi, but there's adult content to be had and it's pretty dark.

Quote from Sagaris

Eden (ENDO Hiroki)?

Not really ecchi, but there's adult content to be had and it's pretty dark.

Nice. Cyberpunk + Dystopia + Post-Apocalyptic? Good combination.

In a world where troubled young hearts are besieged by evil spirits, only one can wield love as a weapon: the God of Conquests, Keima Katsuragi.

Maybe you'll like these:
Space Adventure Cobra
Trans Venus
Muvluv Unlimited and the other related series, like Muvluv alternative

7 Billion Needles
Appleseed
Noise the prequel to Blame!
Blame! over the oneshots based off of it.
Biomega from the same guy who did Blame!
Boogiepop Doesn't Laugh a little sci-fi mixed with some fantasy. It's pretty crazy.the reason I'm recommending it, is because the series as a whole including the books and the anime make it lean more into the sci-fi genre.
Gantz duh
Junk - Record of the Last Hero think sentai if it happened in the real world.
Mardock Scramble
Zipang don't know if you can classify mysterious time traveling incident as hard sci-fi. But it's a good read.
A Certain Scientific Railgun it's in the name even.
Battle Angel Alita
Definitely second Eden: It's an Endless World! that shit is legit.

Anyway, sci-fi/ecchi is not a very common genre.

Sarcasm just doesn't work over the internet.

I wouldn't call it 'hard' science fiction, but Fire Candy might float your boat.