Excel

[From JanimeS]:

EXCEL is about a relationship between two sisters, Anri and Anji. Anri is one year older than Anji. Anri is a person with determination and guts, not to mention top grades and attitutde. Anji is a person with really nothing to offer. Anji can be quite mean and unreasonable. But, when it comes to down to her sibling, she can be pretty determined.

The story details the troubles that Anji has to go through because of Anri's two-faced boyfriend, Baek-Hui Kang.