Aria the Scarlet Ammo: Caged Bird

Field trip has finished. Along the way back to Tokyo, someone had planted a bomb within the bullet train where Kinji and the gang are boarded. Not only the bomb will explode if the train's speed is decreased, but they must increase the speed by 10kph every 3 minutes or it will explode. Even worse, Riko had deduced that the culprit is also inside the train! This mission calls for Kinji, Aria, Riko, Shirayuki and the other Buteis present in the train to disarm the bomb and save the passenger. And they've only got 80 minutes until the bullet train reaches Tokyo.