Aria follows Kinji to the arcade where he manages to win some plush dolls for her. The next day, Kinji and Aria learn that a schoolbus has been hijacked by the fabled Butei-killer and fitted with a bomb that will explode if it slows down with an armed convertible preventing the passengers from interfering. As the busdriver gets injured when an attempt to stop the convertible is foiled by heat-detection, Aria and Kinji arrive on the scene, taking out the convertible. With the bus slowly running out of gas, Aria finds the bomb on the underside of the bus whilst Kinji finds and destroys the communications sensor. The bomb is disarmed by the sniper ace, Reki, but Aria is injured by another armed vehicle whilst trying to protect Kinji. As she is treated in hospital, she feels disappointed that Kinji didn't meet her expectations.
Kinji approaches the training facility of Assault to fulfill his promise to Aria, and encounters Riko as he ponders on his incoming mission. After a short talk with her, he receives a ticket for free coins at the arcade; for some reason, Riko has been keeping it between her breasts, and Kinji has to look away, although he has managed to catch a glimpse of her yellow underwear...
After Riko leaves, he receives an unexpected welcome from a few students of Assault, including Ryou Shiranui. Their teasing comments about his return to Assault is then interrupted when Aria appears.
Kinji notices how her presence has caused the students of Assault to run away, and Aria tells him that it happens all the time. Kinji then wonders if her name has anything to do with it, especially since an aria is a solo performance, and asks Aria if her plans of making a slave out of him is part of turning her solo career into a duet. Aria thinks that Kinji is trying to be funny, but he is actually serious.
He then decides to go to the arcade alone and asks Aria to go home. However, she decides to follow him, and even sprinting is not able to shake off Aria that easily.
A tiring race later, Aria and Kinji reach the arcade.
Almost instantly, Aria is attracted to a claw crane filled with white plush cats. Unfortunately, she does not know how to operate a claw crane, and Kinji decides to teach her. After several tries, Aria fails to grab a plush cat properly and is starting to become frustrated, and in the end, Kinji decides to try himself.
To his surprise, he got two plush cats for Aria.
As they head back home, Aria is clearly overjoyed by the cute toys Kinji has picked up for her, and even gives one to Kinji. Kinji does not expect that Aria, the girl who has tried kicking him in his crotch once, is now a cheerful girl in front of him.
That night, he arrives at home, and notices that his watch is five minutes in advance.
He sets it five minutes back, and at the next day, realizes that he might have made a mistake in setting the time. As usual, he misses the 7:58 AM bus. Meanwhile, as Kinji stops chasing the 7:58 bus, a message from one of the passengers in that bus receives a call that declares that there is a bomb inside the bus.
Kinji discovers about what is going on when he receives an urgent call from Aria, and he rushes to school, where he and Aria board a car to pursue the bus while filling him on the details including the fact that the Butei Killer is still at large.
Meanwhile, the bus in danger, which Ryou and classmate Gouki Mutou board along with several other students, is soon pursued by a yellow sports car with an Uzi mounted on its driver seat and, after firing several warning shots, orders the bus driver to do not slow the vehicle and gradually increase speed over time.
Aria guesses that the Butei Killer's target is Odaiba, and Kinji thinks that it is possible, since as an area with a large population, the Butei Killer plans on hindering any Butei unit's movement by moving through more populous areas. Aria is amazed at Kinji's ability to understand her thoughts, and wishes that he reveals more of his hidden potential.
Inside the bus, the students have decided to fight back, although Ryou warns them to be cautious of their plans. One of the students devise a plan to disable the car, while they approach an incoming tunnel by shooting at it, while the security camera mounted on the car is still readjusting to the changes of brightness.
They proceed to their plan, however, they discover a shocking fact that did not consider: Heat detection.
The moment the three students unleash their attack, they are knocked away by the rain of fire unleashed by the mounted Uzi. What's worse, the bold attack also incited the Butei Killer to attack through the students inside, severely injuring the driver of the bus and hurting the students inside, who are fortunately protected by their bulletproof uniforms.
Gouki is forced to replace the injured driver on the steering wheel, and when the Uzi attempts to target him, a gunshot is heard, and the Uzi is released from its mount.
It turns out that Aria and Kinji have reached the bus, and Aria fires at the sports car's tires, causing it to spin out of control. As the car explodes behind her, Aria boards the car once again and tells Kinji that they should defuse the bomb. Although Kinji has doubts, Aria pushes through with the plan. After tying the steering wheel in place, Aria and Kinji hop on to the bus.
Aria and Kinji split up to look for the bomb. While Kinji checks up on the driver's seat, Aria hoists herself using a length of rope and peers at the chassis, where she sees the bomb. Aria assures Kinji that it can be dismantled, but there is still the problem of an existing link between the bomb and the Butei Killer, which Ryou addresses. He asks Kinji to look for and dismantle the sensor that is sending out information to the Butei Killer.
Meanwhile, Aria is still having difficulty reaching the bomb, and soon scolds Kinji for going outside. Fortunately, Kinji has pulled out the sensor. However, there is another problem for both of them: another sports car with a mounted Uzi has approached them. Kinji is unable to respond as the Uzi opens fire, and Aria decides to shield him from the gunfire.
Aria manages to pop one of the car's wheels, but she has sustained a few wounds and lost conciousness.
Soon, a chopper flies above them as the bus arrives at the Rainbow Bridge. Kinji instantly spots Reki on the helicopter, and watches as she prepares to take a shot at the bomb under the bus. The shot itself is challenging; as the helicopter hovers and maintains the same speed as the bus, there is still the many steel rails that line both sides of the bridge, not to consider many factors that make things too complicated.
Nonetheless, Reki fires at her target, and she succeeds, dislodging the bomb from the underside of the bus and knocking it into the sea. A large explosion soon follows.
That afternoon, Kinji visits Aria at the infimary and meets Reki. It turns out that Aria is Reki's client and her intervention is part of her deal with Aria.
Kinji soon reaches Aria's infirmary room and has to listen to her bickering about being hospitalized for such a minor injury. He then hands out a report about the incident earlier and mentions that they could not find any clue about the "Butei Killer", but Aria just throws it away and asks Kinji to leave.
As Kinji prepares to leave her room, Aria wonders why he hasn't displayed the ability he has shown to her earlier. In response, Kinji tells her that it is bad to force expectations on a person, and reminds her that he has decided to quit being a Butei.
As Kinji closes the door behind him, Aria feels disappointed, not being able to find the one that she has been looking for.
- The bomb on bus is actually an reference to Speed (1994)
- "So, you plan to make me your slave and turn it into a duet?" — by Kinji Tohyama
- "I am a single bullet..." — by Reki