The novel is on the R18 version of syosetu. The normal syosetu has r15 and lower but the adult stuff is on the r18 side.
The reason the Mc is like-able is because he is not a complete douche. He really does care about Kenji but he cannot help but feel suspicious of the world’s natives. He knows the world is a game set up by some higher being and he cannot help but think that all the NPCs are in on the secret.
This is what makes him an anti-hero. He lacks the heroic traits of idealism, courage and morality; all things Kenji has in spades. MC does not lie about his weaknesses, he constantly tells Kenji not to trust so easily, Mc just wants to go home he does not care about the country they are in, and he is not above using drugs to get the truth from those he is suspicious of or seducing them.
But Mc never lies about this to the readers which is why he is still a like-able character. He won’t go the other side of the country to save a village but he won’t let a village be burned in front of him.