Hanazono-san Chi no Futago-chan

Tatara Tani is so average it hurts—the only thing he has going for him is that his childhood friends are ultra-popular idol Yuriko Hanazono and her fashionable twin, Ranko Hanazono! They're both his classmates, and his long-standing relationship with them makes others seethe. So he thinks he's hit the jackpot when Yuriko asks him to the amusement park with her, even though idols aren't allowed to date. She dresses up as Ranko to fool the world, but when her ruse is discovered by the school, it's up to the REAL Ranko to save her sister's reputation...by dating Tatara herself? This crazy rom-com of errors begins!

(Source: Kodansha USA)