BJ is a mysterious robot in the video game '13 Sentinels: Aegis Rim' developed by Vanillaware. Unlike other characters, BJ is not a human but plays a crucial role in assisting the protagonists. It initially appears as a small, round robot with limited communication abilities, using only beeping sounds. However, as the story unfolds, BJ's purpose becomes clearer, revealing its connection to the larger narrative involving time travel and the defense against an impending apocalypse. BJ provides critical information and guidance to the characters, helping them navigate complex scenarios.