I really recommend Darwin's Game it's really good!
http://www.mangago.zone/read-manga/imawa_no_kuni_no_alice/
http://www.mangago.zone/read-manga/btooom/
http://www.mangago.zone/read-manga/battle_royale/
http://www.mangago.zone/read-manga/deadman_wonderland/
http://www.mangago.zone/read-manga/area_d_inou_ryouiki/
http://www.mangago.zone/read-manga/mirai_nikki/
I liked Cage of Eden
Literally attack on titan hahahaha jk
Would love some recommendations for works similar to suicide island, death tube, danganronpa or though you may burn to ash. Something that makes me care about the characters, only to kill them. Gore/romance is highly appreciated, but not necessary.