While not playable, understanding the key supporting characters is vital for the story and sometimes for gameplay mechanics:
- Haruka Sawamura: Kiryu's adopted daughter, her accident is the catalyst for the entire story.
- Haruto Sawamura: Haruka's infant son, whose paternity is a central mystery.
- Makoto Date: Kiryu's long-time detective friend, providing crucial information and support.
- Yuta Usami: A young member of the Hirose Family, who becomes a close ally to Kiryu in Onomichi.
- Toru Hirose: The patriarch of the Hirose Family, a seemingly unassuming old man with a hidden past.
- Nagumo, Tagashira, Matsunaga: Other members of the Hirose Family who assist Kiryu in various ways, often joining him in Clan Creator.
- Tsuneo Iwami: The powerful head of the Iwami Shipbuilding company, a major antagonist.
These characters drive the narrative and often provide context or assistance during missions. Their relationships with Kiryu are central to the emotional core of the game.