That ship gets confusing when people use Railgun's last name but Mental Out's first name. Ship should be named Misaka x Shokuhou, or Mikoto x Misaki (or Misaki x Mikoto)
^ In this artist's previous Marisa x Shanghai art, Shanghai was enlarged, but still a doll.
Given the number of people in Gensokyo who can basically reshape reality to their will, a living doll getting a human pregnant seems entirely possible.