Sae Niijima is the older sister and legal guardian of Makoto Niijima since their father's death a few years prior. She work as a public prosecutor of the Tokyo District Special Investigation Department at the Public Prosecutors Office. She wishes to reform the legal system, envying the Phantom Thieves for achieving that when she struggles and fails due to her superiors' corruption. She's intelligent, has overworking tendencies, struggling to act her age.