Anime Overdose is a special driving event.
This event will happen while driving after Anime Girl has reached her final degradation stage, making her explode and dealing 2 points of damage to every other character. Only the first point of damage is lethal, meaning characters with 2 health will survive, but characters with 1 health will die from this. This event will not happen if Anime Girl explodes in the overworld during scavenging missions.
If Anime Girl is the only member in your party or if every other character dies as a result of the damage sustained, the run will end in a game over.
Having Anime Girl explode in this event is the only way to get the 'Anime Syndrome' achievement.