Spoilers: through "Countrycide" in Torchwood.
In Four Things Jack Never Would Have Guessed About Ianto, and One Thing He Suspected,
ninefics makes
a beautiful character study of Ianto which weighs in at a lean 1550ish words. Thereby making my list of "people whose brains to eat and thereby gain magical powers."
It cost him nearly a hundred pounds, two promised dinners, and four rounds of drinks before Jack finally admitted that Ianto has an almost supernatural ability at billiards.