Liar Game - Roots of A
Roots of A is essentially a manga short featuring Akiyama during his senior year of college. In it, Akiyama and four of his classmates are taking a criminal psychology course and given an assignment where they must construct a profile of a person based on a letter they sent. This outcome of the assignment, plus what the professor says afterwards, is what prompts Akiyama to enter grad-school and continue to study psychology.
[Side Story of "Liar Game"]