The Third Chairman is a High School Girl (2012)

Sinopsis

High school girl Ruri is reunited with her twin sister Sakurako, who has led separate lives, for the first time in 17 years. The two, who have nowhere to belong to each other, switch places for a limited period of one month, but to their surprise Sakurako is the third head of the Todo clan. Ruri struggles to protect the clan from rival yakuza...