Miki first meets Arimi when she’s at Wonder Dog with Yuu, and the first thing she notices is how pretty Arimi is. Yuu introduces her as an “acquaintance” from junior high. Arimi asks for Yuu’s new address and phone number, and is polite to Miki. After she leaves, Yuu informs Miki that the two of them used to go out.
After Miki gets into a fight with Ginta, she goes out of her way to avoid him, and when she sees Arimi waiting for Yuu outside of their school, she takes Arimi by the arm and drags her away (just so she won’t have to talk to Ginta). She and Arimi have tea at a cafe and Arimi tells Miki the story of how she and Yuu dated.
In junior high, Arimi was attracted to Yuu right away, and asked him out, but he turned her down, telling her that he just wasn’t interested in dating anyone right now. Arimi anticipated his answer, and he asked why she asked him anyway, if she already knew. She said because she’s confident that the two of them would be perfect together.
“Give me three months, that’s all the time I need. I know you’ll see what a perfect couple we are. If after three months you don’t think I’m your dream girl, I’ll just walk away and never bother you again.”
Yuu accepted and they dated for three months, but at the end, he broke up with her, stating that he can only see her as a friend. Arimi was devastated.
She admits to Miki that she still loves Yuu, and that she’s “not going to lose.”
Arimi shows up in the second volume at Miki’s school festival, because Ginta is playing tennis against Arimi’s school. The rival player is Tsutomu Rokutanda, Ginta’s cousin, who also likes Arimi. But Arimi insists she’s only interested in Yuu.
After suspecting that Miki might have some leftover feelings for Ginta, Arimi convinces Ginta to pretend to go out with her in an attempt to make Miki jealous, stating that it will help both of them get the person they want. They fake-date for a while but Ginta can’t keep up the act, and tells Miki everything. Arimi apologizes, but also states that Miki doesn’t deserve Yuu even though Yuu might like her.
Arimi continues to pursue Yuu through the fourth volume, but eventually gives up when it becomes clear that he loves Miki. She even goes as far as to say she’s happy for him that he’s finally in a real relationship. She painfully lets him go.
Eventually, she and Ginta fall in love and become a couple.
Personality:
Unlike the other girls in the story, Arimi isn’t content just sitting around waiting for a boy to make the first move. She is aggressive and not afraid to go after what she wants.
On the downside, she can’t give up easily, even when she has already lost. Despite telling Yuu when she first asked him out, that if it didn’t work out, she would never bother him again, she DOES continue to bother him and tries to be his girlfriend again. She displays somewhat stalker-ish behavior towards other characters, and has a competitive streak.