With Kadokawa have been teetering recently, perhaps we will see less Isekais in the future, but I still come across to a promising one on a random encounter of manga called Nigoru Hitomi de Nani wo Negau: Highserk Senki. Dark Fantasy rarely blends with Isekai but Highserk Senki is one of those few specimens. Just like typical Isekai series, the main protagonist died once and transported into a Fantasy Medieval settings that just happened to be bleak one where War is a common occurence. The main Protagonist is an Anti Hero who served a warlike medieval Kingdom called Highserk and slowly rise from the rank of Common Soldier with his special ability and Magical talent of Blue Flame which had a peculiar significance in the setting and spread terror upon his foes.
Highserk Senki is quite a fresh Isekai reading experience since the amount of the Grimdarkness of the setting hit the right amount o balance without being too edgy. The main Protagonist also is not really a wuss either like typical Japanese Isekai protagonist who tried his best to stay in a Neutral alignment despite going through a hellish experience while keeping himself grounded and do whatever necessary to stay alive. So far the Manga only had 19 Chapters but the Light Novel translation had been going quite far which the Manga only reached about 1/5th of the Novel translation. I probably will binge the Novel and keep track of this series if It can wrap up with Satifsying ending which many of Isekais failed to do.