Mio's life is changed in a big way due to an encounter with Rin, an upperclassman who is one year older, and...!?

From JShojo:

Aki has always liked her basketball club friend, Mase. However, she can’t seem to gather her courage to confess to him. On the day when she finally decides to tell him, she is confessed to by a guy from a different Junior High!! A horrible accident follows and Aki finds herself not being able to choose between the two – Mase, whom she truly loves or Koichi, whom she’ll always feel indebted to…

Story 1: Christmas Version - Aki wants to go on a trip with Mase, but they have no money for it so they decide to get a part time job. Unfortunately, not many are ok to hire high-school kids. Aki gets a job at a bar owned by Mase's brother, that doesn't think she is worthy of being the girlfriend of his little brother. She is determinate to prove him wrong and spend the best Christmas with her boyfriend.
Story 2: Passion Pink Version released in Genshoku Tsundere Danshi Semekare.
Story 3: Koibana Confession.
(Source: Chibi Manga & Evil Flowers)

In order to put a period to a love where she only looks at the guy she likes, Sayumi decides to confess to her beloved Yui-kun! Thanks to her forceful action, they start dating. Every day, as she gets to know more and more about Yui-kun, she falls in love with him more. However, there's someone who he'd turn to look at every now and then...
(Source: Aerandria Scans)

Sixteen-year-old Nene Kashiwagi has undergone a transformation from a sporty girl to a chic one--or, at least, she's trying to become chic so that she can finally find love! Her efforts only gain her teasing from her (former) friend, Jun Endou. But when Nene's first attempt at finding love goes awry, Jun steps in to rescue her in the most unexpected way.

Shuusei Kugayama is the "prince" of his high school, but he always turns down confessions—including one from Aoi Nishimori's best friend. Although she initially hates him for this, when Shuusei moves in next door to Aoi, who lives alone, she starts thinking that he might not be such a bad guy after all...
(Source: Which Scanlations)