Yondome wa Iyana Shizokusei Majutsushi

Yondome is a series that would probably be traumatic to watch but is ideal for reading.  I say this because the things done to the protagonist and he does to others are pretty horrifying from an objective perspective.  He spends most of his first reincarnation being tortured as an experimental subject, his magical energy drawn out to make convenient tools, and his second reincarnation has him cursed and living his life surrounded by undead of his own making.  

However, for someone reading this story, it is surprisingly touching at times, with interesting and amusing characters.  Yes, imagining a lot of the scenes is pretty guro and reminded me of Tokyo Necro.  However, the story of Vandalieu has become quite dear to my heart.  Most likely because of how ingenious the author's portrayal of Vandalieu's life is.  It is proof positive that there are things you can get away with when writing that would only alienate people watching an anime.

Sacchi Sarenai Rule Breaker

Rule Breaker is your standard 'protagonist is overpowered and has an absolute advantage' series, with the twist that he has a solid girlfriend almost from the beginning.  Hikaru is an unusual character type, in that he is someone who is a bit overly impressed with his own cleverness, but he is aware that this quality is a personality flaw.  The story itself has Hikaru sorta-kinda reincarnating into the body of a guy who tasks him with avenging his death inside one hour by killing a local nobleman.  Hikaru, in order to succeed, uses his new ability - the Soul Board - to specialize in stealth so he can get away with it.  

This essentially begins a story where the protagonist essentially does amazing things because he is overspecialized to an insane degree in stealth and detection.  Unlike a lot of stories of this type, where the protagonist is exceedingly capable in all areas, Hikaru is definitely a min-max character for most of the story.  His personality is also one that some people will have trouble with, but on the flip side, he has a lot more foresight than the average isekai protagonist and actually manages to keep his public persona in the background, something few overpowered isekai protagonists can manage.

Kuro no Maou

There is only one phrase that sums up Kuro no Maou... 'Yandere Harem in another world'.  The protagonist of the story, Kurono Maou (lol, yes his name is a pun) begins the story as a fierce-looking but kind-hearted high schooler... until he is summoned to another world to be experimented upon by a bunch of religious fanatics to turn him into a black magic using living weapon. Counter to tradition, he manages to break free only after losing a surprising amount of his humanity.  By the time he gains his freedom, he has killed other people on numerous occasions, including other summoned Japanese people.  He also loses the ability to hesitate when killing is needed, which cuts off one of the more annoying character tropes that tend to follow around isekai protagonists.

The author describes Kurono as a 'Yandere Seizouki' (a yandere-producing machine) because he is not only dense but somehow manages to say and do the right things to tip girls over the cliff into yandere-ism.  While this is highly amusing, it also means that even the SOL toward the middle and end of the story is quite a bit more stressful than is common to fantasy and isekai.   Moreover, his density is made worse by the fact that his magic mastery actually suppresses his sexual desires, meaning he mostly just fails to notice the girls are aiming for him for most of the story, despite them being rather obvious to people looking at the situation from the outside.