Moonlight Garden is has a lot of dark themes and a good plot, but it's pretty fluffy at times too
http://www.mangago.zone/read-manga/gunjou/
http://www.mangago.zone/read-manga/vengeance/
These are the two best I can think of right now.
There's also
http://www.mangago.zone/read-manga/the_chain_of_youth/
It's short and more of a drama but not fluffy at all. The only problem is that you have to buy the last two chapters because nobody has uploaded them yet and the comic isn't available for free anymore.
I want to read more yuri but I'm not really into really fluffy stories at all. Anyone have any recs for ones that have darker/psychological themes to them and a good, interesting story??