(No harem, no brainless characters, no System, no invincibility, and no power-fantasy wish fulfillment. Read with caution if any of that bothers you.) There are lighthearted little episodes that may leave you baffled but won't hurt your brain, so the story won't get too oppressive.
I woke from a nightmare and found myself in this strange place.
It is rife with murder and betrayal. Every ordinary person is a weak insect. To escape, you have to take part in the Myriad Phenomena Game.
Or you can offer up your soul, gain the power of immortal arts, erase your memories of the past, and rise above everyone else in this land.