Idol Hakkenden: Minami no Shima no Taiyou to Hoshi

Sick and bedridden, the zaibatsu tycoon Tomiko senses that her death is near and must nominate an heir among her three granddaughters. To decide who will receive her whole fortune, she launches a challenge: whoever will give her best in the next three months will be the winner. Shizuka, the oldest granddaughter and owner of several business companies, and Reika, the second oldest and a genius scientist, are sure that it's going to be a battle between the two of them. However, Erika, the youngest, has a plan of her own: using her only talent, singing, she aims to break through as a super idol and to do so, she must first seek the help of seven other companions.

(Source: Wikipedia)