Apocalyptic ones;
https://www.mangago.me/read-manga/undead_tsuyuhisa_fumi/
https://www.mangago.me/read-manga/a_room_without_space_side_story_1/
https://www.mangago.me/read-manga/believe_my_sign/
Little mushroom
Rainbow city
Tragic and/or sad with happy ending:
December rain
Murderer Llewellyn's enchanting dinner invitation
Tragic and sad NO happy ending:
10 years where I loved you the most
Lucky letter
Haruka Tooki Le(Home far away just under diff title)
Perle(sad and historical)
stay alive is still ongoing and has a novel that goes into better detail but if you like an outbreak story? this one is great since at one point the fucking korean government itself basically says over a tv boardcast that we’re all fucked gang! so get your ass to a certain part of korea so we can safely gtfo since we agreed with the un itself to missile strike the shit out of korea in a month lmao
https://www.mangago.me/read-manga/let_s_meet_alive/
dreadful night is also ongoing but on a hiatus I think..? but tldr is that mc is stuck in a slasher horror video game time loop with several other boys
https://www.mangago.me/read-manga/dreadful_night/
Haiii !! I recommend reading the 11th school trip!
https://www.mangago.me/read-manga/the_11th_school_trip/
It's currently ongoing and updates every week! It also has a novel, if you want to read it you can go check out on :
https://cherrymist.cafe/chapter/est-ch-9/
also two more recs:
dear door is fucking great in the art department since it’s all about demons among other things, but it’s heavy on the smut later on, and the ending kinda feels abrupt per say depending on who you ask
https://www.mangago.me/read-manga/dear_door/
https://www.mangago.me/read-manga/madk/
madk.. honestly? this is an optional rec since genuine tw if you can’t handle heavy gore among other sensitive topics since it’s infamous and popular for a reason but right from chapter 1 is uh.. oof is what I can say best
if you can stomach it? the ending is a subtle masterpiece once you realize what it means
tldr: madk is the equivalent of watching smile hd (iykyk) for the first time, aka oh.. this is fine, it’s cute and— oh shit wait what? did she just— what the fuck is going on

Dark fantasy plots, survival scenarios (zombies/apocalypse), or perhaps gritty realism that includes tragic endings, painful time travel, or social conflicts like homophobia and arranged marriages. Any of these are fine ( ̄∇ ̄")