Kouichi and Mao are childhood friends, but as they enter High School, they become more and more distant. And as Mao becomes more popular and beautiful, Kouichi wishes he could be popular too, and eventually get a girlfriend. Mao decides to help him...

Based on a bishoujo game.

As per the title, "various heroines", each volume of this manga focuses on a different girl Kouichi can eventually end up with.

Homura Tsukishima and Sakurako Hirosue are roommates at Principia Academy, a school located on an island created specifically for researching "shiki", which is a form of power created by manipulating numbers.

Two years ago, Tachibana Junichi got his heart broken by a girl who didn't show up for a date on Christmas Eve. Now a second year student in high school, Junichi spends his days inside his closet planetarium, going to school and hanging out with his friends Tanamachi Kaoru and Umehara Masayoshi.
Volume 1-2: Ayatsuji Tsukasa arc
Volume 3-4: Tanamachi Kaoru arc
Volume 5: ?

Shun knew what to expect when he became a high school student. As he entered the gates of his new school, four beautiful girls suddenly surround him. These four girls are the same four girls he grew up with since kindergarten. The four girls are Rio the athlete, Miku the cook, Nana the nerd, and Yuri the student president. These four girls will be battling it out between them in order to win the heard of their beloved Shun. [DrCoke]

Source: MU