At the Morisato residence, Keiichi is building a computer and Urd is watching TV. Skuld is busy constructing a machine to protect them from Mara and is bothered that no one else seems concerned over her return. She puts the finishing touches on the machine, connects it to the temple's power grid, then activates it causing all of the power in the temple to die. Both Urd and Keiichi are upset with this and go to find out what Skuld is up to. It is here that she shows them her anti-Mara tactical strike robot named Mini-Banpei RX. Neither is impressed causing Skuld to cry. Banpei becomes alert and brushes past an alarmed Urd to go outside where Belldandy is.

In the sky above the temple, Mara sits and observes the lack of valiance on the part of the Morisato clan. She attempts to summon Senbei from his bottle, but he refuses. He doesn't like Mara's plan to have Keiichi drink him and won't go along. As they argue, Belldandy spots Banpei who in turn has locked onto Mara. Mara becomes aware of him just as Banpei launches an attack, sending a stream of good luck paper charms her way. All of them hit the intended target.

Urd hears what happened and is impressed. After praising Skuld, she strongly suggests turning the robot off so that she can watch TV. Skuld is reluctant, but puts Banpei in standby mode before going inside. Belldandy sees the still Banpei and doesn't know why he's been put into standby mode. She reactivates him causing another power failure in the temple much to Keiichi and Urd's displeasure. Belldandy decides to solve the power problem by magically creating a new booster circuit. She does so and is wiped out from the attempt. However, Keiichi is there with a fresh moon bracelet and an apology for being upset. Together, they continue working on the robot.

Once completed, they reactivate Banpei who does not cause the temple's electricity to go out. Their celebration is short lived as Banpei begins attacking Keiichi, forcing him off the temple grounds - the length of his power cables. Skuld can't understand it until she runs a diagnostic and sees that Banpei was able to change is programming from the circuit board Belldandy made. His new directive is to protect Belldandy from everyone. Urd has had enough and attempts to turn off the robot. This causes Banpei to attack Urd!

Later, Banpei brings Belldandy a cup of tea. She tells him "thank you" which the robot plays over and over in his memory. Keiichi and Skuld don't know what to make of this, but Urd suspects Banpei has fallen in love, despite the fact that Skuld did not create an emotion circuit. This is the effect Belldandy has on everything around her.

The following day, Banpei watches Belldandy make a lunch for herself and Keiichi. Keiichi is in a hurry to leave before Banpei can attack, so he hurries Belldandy into the sidecar causing her to leave the prepared lunch on the counter. They leave and Banpei sees the forgotten lunch. He replays her saying "thank you" to him, then grabs the bundled lunch and heads outside. Once he reaches his power cable limit, they snap off and he transforms into a cycle mode and goes to Nekomi Tech. There, Keiichi explains to Belldandy what has been going on with Banpei when he nearly runs into him. With his last remaining battery power, he holds up the lunch and tells her she forgot the important lunch. His power failure caused the special program he created to be erased. However, Belldandy continues to hope that somehow a tiny piece of that program still resides in Banpei.