In this world, like most fantasy worlds, there are different races.
As usual, there are elves; this is what's known of them.
Elves are biologically much more slender than their human counterparts. Both the men and the women seem to have small sizes in terms of their private parts. Although there is individual variation in size, when having sex with a human male, it cannot be compared to having sex with their own species, and there is this extremely sensitive spot that is unbearably pleasant to them, and it can only be reached when an elf’s most interior womb is vigorously stimulated.
It seems that one of the reasons why half-elf’s appear in this world is for such a pathetic reason; Tooru really do sympathize with the man-elf’s.