Kuroto reveals Patient Zero

Realizing that his former ally's wish is to defeat Emu Houjou, Kuroto Dan decides to crush Parado's wish by personally telling Emu the truth behind why he's able to transform or why he has migraines: He was Patient Zero of a video game-related sickness known as the Bugster Virus (a truth that everyone including the audience knew) and, as soon as he realizes this, Emu glitches out of reality...

Example of:
Villain Reveals the Secret