Toki Nazumi, Futari Nazumu

From Amaranth Scans:

Haruhi, Shinogu and Moe are sixth graders from the same elementary school. Moe and Haruhi are said to be polar opposites as Moe is Shinogu’s gentle and caring childhood friend, while Haruhi is Shinogu’s lively classmate.

Shinogu suddenly decides to attend a private junior high school that Moe is going to attend, and Haruhi finds out the reason why. Fast-forward by three years, what will happen when Haruhi enters the same school?

Includes an extra story (chapter 5):
Ribbon of Love