Which of the following was NOT a playable character in the game Kingdom Hearts: Birth by Sleep?

The correct answer is Ignis. Ignis is not a playable character in the game Kingdom Hearts: Birth by Sleep. This game features three main playable characters named Terra, Ventus, and Aqua, who embark on separate journeys to uncover the secrets of their world. Ignis, on the other hand, is a character from the video game Final Fantasy XV and does not appear in Kingdom Hearts: Birth by Sleep.