Urukyuu

From Tokyopop:

For all 15 years of their lives, Ami and Noa have competed against each other for love with the same results: both fall for the same guy, inevitably scaring him away and leaving them boyfriend-less. But the vicious cycle is broken when the girls go to a party and each fall for two different guys! With potential love on the horizon, the sky couldn't be bluer...until Ami discovers that these two dudes are actually duds with ulterior motives. Determined to get revenge on these players, Ami vows to make her guy fall for her while she trys to protect an unsuspecting Noa!

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Bitter rivals since kindergarten, Ami and Noa are always fighting over the same boys. Neither of them ever succeeds in getting their man and neither has ever had a boyfriend. Ami and Noa are 15 years old when they meet two cute guys called Tamon and Hiro. This time it is different: They don't fall in love with the same guy. Ami fancies Tamon. Noa likes Hiro. These guys, however, are a pair of crafty rogues, playing what they call "a harmless love game." Enter Mika, Tamon's ex-girfriend, and Miyamura, a weird teacher, both out to spoil Ami and Noa's plans.