Koishi Tagari no Blue

Fifteen-year-old Ao Mizushima has always made the wrong choices. On her first day of high school, she decides to change things but ends up getting lost on her way to school and literally stumbles into a boy named Riku Hariya. He had just gotten into a fight with a friend, and when Ao comforts him, he asks her to be his fake girlfriend.

Ao refuses and runs off to school, where she sees a girl sitting by herself in her homeroom. Her name is Kiyono Soratani, and a girl wards Ao from befriending her, as rumors go that Kiyono snatches boyfriends. Ao befriends Kyono anyway and learns that Kyono was confessed to by a guy who already had a girlfriend and rejected him--thus starting the rumors that it was her who made a move on someone else's boyfriend.

Ao then meets Kai Midou, a popular boy in her class, who is the "friend" that Riku has been fighting with. Riku explains to Ao that Kai accidentally saw a photo of Riku, Kai, and Kai's girlfriend and assumed Riku likes Kai's girlfriend, and he broke up with said girlfriend shortly after. Riku wants to make amends and the only way he can think of doing so is by showing that he already has a "girlfriend"--aka Aoi. Aoi then decides to pretend to be Riku's girlfriend in order to help him fix his friendship with Kai.

This series provides the following tropes:

 * Amusement Park: Chapter 3.
 * The Beard: What starts off the plot--Riku asking Ao to be his fake girlfriend.
 * Chick Magnet: Kai.
 * The Faceless: Kai's perverted friend Yoshida.
 * Ferris Wheel Date Moment: Between Riku and Ao in Chapter 3.
 * I Want My Beloved to Be Happy:
 * In spite of liking Kai's girlfriend, Riku wants Kai and his girlfriend to make up.
 * Kiyono keeps her feelings a secret out of the sake of her friendships with both Ao and Riku.
 * Indirect Kiss: Riku purposely tries to invoke by taking a bite out of the same bread Ao did, but she shoves it all in his face before he can.
 * Les Yay: Upon befriending her, Ao sure thinks Kiyono is cute, pretty, and that even she feels "captured while looking at her." It's even lampshaded by Kai, who arrives when Ao is asking Kiyono how she feels about her (as Kiyono doesn't believe anyone likes her).
 * Love Triangle: Riku has a crush on Kai's girlfriend, and Kai broke up with her because of that.
 * Meaningful Name: Ao means "blue" in Japanese.
 * Plucky Girl: Ao.
 * Red Oni Blue Oni: Riku and Kai.
 * The Reveal: Kiyono is Kai's ex-girlfriend.
 * School Idol: Kai.
 * Short-Haired Cutie: Ao.
 * Tall Dark and Bishoujo: Kiyono.
 * Tall Dark and Handsome: Kai.
 * Three Amigos: Riku, Kai, and Kai's girlfriend.
 * Unwanted Harem: Kai and Kiyono.
 * Three Amigos: Riku, Kai, and Kai's girlfriend.
 * Unwanted Harem: Kai and Kiyono.