Aria demands that Kinji join her Butei party, intruding in his living space when he refuses. This puts Kinji in an awkward situation when his childhood friend, Shirayuki Hotogi, pops over whilst Aria is taking a bath. The next day, Aria follows Kinji around as he takes on a quest to search for a missing cat. After managing to lose Aria, Kinji trades some eroges with his friend, Riko Mine, to obtain information on Aria. Meanwhile, Aria calls Kinji's bluff on his Butei abilities and coerces him to agree to join her on a single Assault case, so she can witness his Hysteria Mode.

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.