Akane had run into an unfriendly punk on the train. Hikaru came up, saved her and tossed him off the train at the next station. She introduced herself as Kyousuke's girlfriend. Kurumi and Manami tell Kyousuke to get ready to go to the pool. Hikaru arranged with Akane to go with them, and made Akane promise to invite Kyousuke too. He says he's already made plans for today. Akane's surprised that he's turning down an invitation from his girlfriend, and that he won't say why. Kyousuke's even less pleased when he hears that his sisters have invited Komatsu and Hatta to join them.
Later Kyousuke and Akane are walking down The Stairs. He tells her that he promised to go play tennis with Madoka, explaining that she's just a classmate who almost like a sister to Hikaru. Akane gets the idea that he's trying to get on Madoka's good side so she'll support his relationship with Hikaru. Komatsu and Hatta come up the stairs. When Akane hears who it is, she makes herself look like Hikaru to them, and clings tightly to Kyousuke. The two guys are surprised at the way Hikaru's acting and tease Kyousuke, ``You two are really hot.'' After they leave, Kyousuke asks Akane what she did. She says she ``got them'' and adds, ``If we put on an act like that in front of this almost-sister person, then everything will be all right.'' Kyousuke realizes that this is exactly the wrong thing to do and runs off, teleporting to escape from Akane.
Kyousuke makes it to the tennis courts but finds that he hasn't managed to lose Akane. He takes her to a cafe, buys her a parfait and then leaves, with the excuse that he has to go to the bathroom. Komatsu, Hatta and the twins find her waiting at the table. It turns out that the tennis courts are right next to the public pool. When they hear where Kyousuke went, Komatsu and Hatta mention that maybe it was just an excuse and he's playing around with Madoka now like he was with Hikaru earlier.
Akane's not too pleased with this and runs after Kyousuke. He's trying to call Madoka and head off this situation, but she's already left home. Akane finds him by the phone and demands he break up with Madoka. She has a very low opinion of her since she knows about Kyousuke's relationship with Hikaru and is apparently trying to steal him away. While Akane continues to berate him, Madoka shows up, apologizing for being late.
Akane takes one look at her and is transfixed. It's love at first sight. She runs up and complements Madoka on her stylishness, lovely hair and other things. She then drags her off saying, ``Let's play tennis together.'' Kyousuke runs off after the two and stops them outside the tennis court. Hikaru picks this time to find Kyousuke. She's overjoyed that he was able to come. Kyousuke doesn't know what to do. Akane tells him to go along, ``your girlfriend is waiting for you,'' adding she'll play tennis with Madoka. Madoka expresses her opinion by nailing Kyousuke in the face with a tennis ball and walks off to the courts. Kyousuke thinks to himself that it looks like the worst possible case is coming to pass.
After playing tennis with Madoka for a while, Akane suggests that they go swimming. She figures that she's got to do something to counteract Madoka's being deceived by Kyousuke's sweet talk. At the pool, Akane turns herself into Kyousuke and walks up to Hikaru, suggesting she put suntan oil on her back. Hikaru instantly agrees, giggling happily, and Akane thinks that, ``this gal really is quite uninhibited.'' Kyousuke gets out of the pool and notices Akane doing this, so he rushes over to stop her. Just as he gets there, Akane teleports away leaving him to fall across Hikaru's back. Hikaru is happy he's this expressive, especially when everyone is watching, but he's not. He's even less happy when he looks up and finds a very angry Madoka looking down at the two of them.
Madoka heads off into the pool. As the next stage of her plan, Akane comes up and appears as Kyousuke to her, saying that now its time for him to oil her back. Madoka's not so sure about this. ``Kyousuke,'' looking lecherous, dives for Madoka just as the real Kyousuke runs and jumps to try and stop this. Madoka ducks underwater to avoid things, and Akane teleports away so she isn't grabbed by Kyousuke. He ends up falling in the pool and grabbing Madoka instead. The two come to the surface with h face in her breasts. Madoka rewards him with a very fierce slap. As he falls underwater from this, Kyousuke narrates, ``The worst possible case has come to pass.''
That night at Disco Moebius, Madoka and Akane are sitting at the bar. Madoka is drinking and Akane trys to stop her, thinking, ``Maybe I overdid it.'' Madoka pauses, with a sad look on her face, but doesn't stop. Several guys stop by and try to pick up these two girls sitting by themselves. Madoka gets up and tells them off, unsteady after her drinking. When the fellows say they're just lonely, that word makes Madoka pause and think, but she still isn't interested and throws a drink on one of them. The guys aren't pleased, grab the gals and decide to have some fun. Madoka is so drunk she can't defend herself normally.
At this point, Kyousuke comes in. He tells the guys to stop, but a couple of fellows beat him up for his efforts. The lead gang member tells Madoka, ``Let's start with a look at that beautiful chest of yours.'' As he starts reaching for it, images of Madoka pass through Kyousuke's head. He yells, ``Don't you dare touch her!'' and lets off an amazing blast of power that shatters all of the lights in the place. This stops the gang, saving Madoka.
Kyousuke narrates, ``My mind was so full of Ayukawa that I don't remember what happened afterwards well.'' The police arrived and took care of things. They really chewed out the gang, but they didn't believe the stories they told about Kyousuke's powers. Madoka was so drunk that she didn't remember them either.
Afterwards Kyousuke and Madoka are sitting by the fountain in the park. He hands her the earring she lost in the fight. She smiles at him, and takes the earring and his hand.
Later, Kyousuke is sunbathing on the porch of his apartment, reading a letter. He comments, ``So, anyway, due to a small typhoon named Akane, the season started out badly, but I had a feeling that the summer of my seventeenth year was only beginning.''