Roots of A is essentially a short manga 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.
Includes other oneshots:
Three Phase - The Forbidden Divination (1)
Three Phase - The Forbidden Divination (2)
The Tale of Shinobu Kaitani's Dog