Both singing for OSTs.

Same release date.

>.< Aigoo! XD O.O :O

• I don't own the video. Credit[s] to the real owner[s] and YouTube   

I don't own this.

http://www.allkpop.com/2012/04/wonder-girls-sunye-girls-generation-member-seohyun-to-release-new-ost-tracks

^Click the one above