Manga by author Sugisaki Yukiru - Status ongoing

From Fallen Syndicate:A tale of mystery and magic. Naito and Yuta Fuuga are twin brothers with very different personalities. While Naito is elegant and good in school, Yuta is athletic and often winds up in fights. Despite this, they maintain a close relationship. When their father turns up missing, both must travel to Dubai in search of him. A mysterious peddler has other plans though, as the twins soon find themselves in the world of One Thousand and One Nights.

Daisuke Niwa is an ordinary, if slightly unlucky, middle school student. On his fourteenth birthday, he comes down with a 'condition' that has plagued the men in his family for three hundred years. When he sees his crush, Risa, he transforms into his alter ego, the phantom thief Dark. Unfortunately, when Dark sees his crush, Risa's twin Riku, he transforms back into Daisuke. The only cure for this craziness is if Daisuke can get Risa to fall in love with him and Dark can get Riku to fall in love with him. But that's going to be a problem, seeing that Riku hates Dark and Risa loves him.

Daisuke Niwa is an ordinary, if slightly unlucky, middle school student. On his fourteenth birthday, he comes down with a 'condition' that has plagued the men in his family for four hundred years. When he sees his crush, Risa, he transforms into his alter ego, the phantom thief Dark Mousy. Unfortunately, when Dark Mousy sees his crush, Risa's twin Riku, he transforms back into Daisuke. The only cure for this craziness is if Daisuke can get Risa to fall in love with him...