Click the thumbnails for the full-size scans.

Cover of volume 1:

Back cover of volume 1:

Splash page for the prologue:

Nagi offers some gym clothes to Hiro, who doesn't have any, and then Hiro fixes Nagi's hair for her. Hiro tells Nagi her hair is pretty, and that it feels nice under her fingers. Nagi replies that Hiro's hands are cold, and that it tickles. Hiro hums as she fixes Nagi's hair, and Nagi thinks to herself that the feel of Hiro's fingers and her quiet humming are nice.
Hiro asks Nagi if she'll be her friend. Nagi thinks it's a little weird that Hiro's asking it like that, but says yes. She also thinks to herself that it's a little childish and, therefore, cute. Hiro has them pinky swear.

Nagi thinks to herself that when she's with Hiro, the flow of time feels different and she feels comfortable.
Hiro fixes Nagi's hair again. Both of them agree that they're on the same wavelength. Nagi comments that if they were a guy and a girl, they'd probably be falling in love with each other. Hiro asks if two girls can't fall in love, which throws Nagi for a loop. Hiro says she was just joking. She then goes on to say that she's acting as Cupid, braiding Nagi's hair for her so she'll look cute for Tsutsui-sensei. Nagi is surprised that Hiro noticed her crush on him--nobody ever has before. Hiro wishes she were in love too, and says she'll help Nagi out.
Nagi asks Hiro about the song she's humming, and Hiro tells her that she used to play it on the piano a lot, but then she got in an accident and can't play anymore. Nagi apologizes for calling up unpleasant memories. She thinks to herself that she was startled by the scary face Hiro made. She won't bring it up again.
Hiro says she'll give Nagi the song as a present, in hopes that things will go well with Nagi's crush. We're then given the lyrics of the song (see here for the original English lyrics).

Nagi plays "Come Rain or Come Shine" for Hiro to try and convince her to take up the piano again, and we get a flashback to the scene above.
Nagi tells Hiro that she really likes her, whether she plays the piano or not; we get lyrics from "Come Rain or Come Shine" in the background again.

Hiro told Nagi she had a crush on a boy and was going to knit a sweater for him for his birthday. She asked Nagi to act as a stand-in for him, so she could practice on her; the two of them even went on a pretend-date.
Now Hiro is nearly finished with the sweater, and she holds it up to Nagi. Nagi protests that she's no help, since she's the wrong size.
Hiro kisses her on the cheek, and asks Nagi to pray for the best for her.
Nagi thinks Hiro's acting strangely, but figures it must just be nerves. Nagi used to worry about what would become of Hiro if she couldn't be there by Hiro's side, but she's realized now that Hiro will be all right--someone will turn up who'll love and protect her. And then Hiro will cherish that man more than anyone else.
Nagi remembers Hiro telling her that she has the most fun when she's with Nagi. Back in the present, Nagi wonders now long she and Hiro will be able to stay together.

It turns out that the sweater was just part of one of Hiro's many twisted plots (trust me, she's a real piece of work)--she gave it to a guy who was interested in Nagi, and put Nagi's name on it. Then when the guy thanked Nagi for it, she was completely confused and told him Hiro made it, which made him think the girls were playing some sort of game with him. This drove him away from Nagi, which was exactly what Hiro intended (though at this point in time, Nagi is clueless about Hiro's true motives).
When Nagi confronts Hiro about it, Hiro says that she's just trying to do what's best for Nagi (her usual defense), and that Nagi will end up falling for the guy. Nagi protests that Hiro couldn't know that, and Hiro replies that she does know: she knows Nagi better than anyone else does.
Hiro wants to help Nagi, and she's willing to go to any lengths to do it (earlier in the manga, another character warned Nagi that Hiro is unscrupulous when it comes to getting the things she wants, and Nagi is clearly no exception).
Nagi tells her to stop. She doesn't understand Hiro's actions--lying about liking a boy, manipulating Nagi's love life... She only wants one thing from Hiro: for Hiro to look after herself and learn to be independent. She wants Hiro to stop yanking her around.