I can't remember the name of the manga, but I remember how far I got. I'm gonna combine at least a couple of chapters of the manga, to start of how it goes.
In the beginning, an army of people (mages, knight, etc.) delves into a dungeon in a search for the boss. it was later they find the demon boss. everybody attack (and I believe) the demon boss was almost defeated. before the hero could kill the demon boss, he pulls a final magic move that shows a bright light, and then someone looking up in the sky (i believe?) in an alleyway of a city in Japan.
The MC doesn't remember anything and walks out of the alleyway, where a drone looks into him, and the person behind the drone is surprised. later on, a couple of officers stops the MC, notice the slit throat, then question the MC. Before any strait answers came out, a high school looking female took the MC out of the officers and into a building. it was later revealed why MC has a slit throat, and how the building uses to be a torture/murder chamber for gang and mafias and such. Before the female had a chance to kill MC, he remembers who he is, where he is originally from, and whats going on. Gaining his memory back, the MC uses his powers to stop the female from killing him, killing her instead. By accident. Again, there is a drone, and this time, the person behind it was shocked.
Later on, MC realizes that he had killed the female unintentionally, not knowing how the logic of this world works. Remembering his abilities, he collects whatever leftover souls inside the building and tries to bring her back to life. It was later that the person in charge of her mission came to rescue her. (Don't remember clearly, but) Dude explains that he is going to bring her back, but she won't be the same. The story of the female killer comes up, explains why she became a murderer. The female wakes up, the boss (looks at/ feels her?) and was like "yup, no heartbeat." Basically female becomes second MC, a strong zombie of sort.
I'm gonna stop there for others to read this manga, as I think I said much, but if this is not enough, here are some things it has:
- a man in jail but has access to information/item you want, for a price
- A magician who wants to know more of the MC and its world
- a pen that is possessed
- a shark plushie that has the soul of the original owner of MC's Body
- a bit of sexual themes too? I can't remember.