Hirasawa is a 'man in black' who used to work for Kido.

Spoiler

After Kido is killed in the Nakamura Shinya's Case, he is later hired by Tosaki to fight Sato. He takes a role as Kei Nagai's mentor.

Spoiler

At the Forge Security building, Hirasawa saves Kei from being beheaded by Sato, which results him to be left alone to fight Sato. After murdering him by hand-to-hand combat, Sato calls him as a 'tough old man'.