Taiyou to Tsuki no Aida de

On the day Sari transfers to her new school, she confesses her love for her cousin Kazuomi. After being subtly rejected, she find out that Kazuomi's best friend Mizuki is also interested in him. Because those two are like the sun and the moon, Sari's determination to be Kazuomi's girlfriend begins to waver. How will this interesting love triangle develop?