CSJH the Grace

From Wikipedia: 

CSJH The Grace is a Korean girl group formed by SM Entertainment. It consists of four members with skills in singing, dancing and also a bit of acting. The quartet debuted in 2005 and since then, the group gained popularity in South Korea and a number of other countries. They are notably popular in Japan, where much of their activity occurs, following the precedent of other Korean-turned-Japanese-celebrity pop stars such as BoA, who is also managed by SM Entertainment.

The Grace had long been known as simply 천상지희 or 天上智喜 prior to the promotion of the 3rd Korean single around the end of 2006, at which point the group changed the name to the current ones to signal the change of the group's style to a more “graceful” one. The old name was usually shortened to TSZX (the romanization of the Mandarin Chinese pronunciation, Tiān Shàng Zhì Xǐ) or CSJH (the romanization of the Korean pronunciation, Cheon Sang Ji Hui), both of which are still widely used to refer to the band despite the change in the official name. The Grace is also known by a variety of other names, as different countries have different pronunciation for the four Chinese letters in the name. In Japan for example, the group is known as Tenjōchiki, which is also abbreviated (albeit less frequently) as TJCK.

The four members are Dana, Lina, Stephanie, and Sunday.

You should check out their music, it's very good.