In 2007, Ye Eun made her debut with the Wonder Girls, a girl group managed by JYP Entertainment, with the single "Irony" as the lead vocalist of the group. She composed the songs "Saying I Love You" and "For Wonderful". Park Ye Eun performed the songs live in one of their U.S. concerts.
In 2012, she wrote a song for the upcoming drama "Dream High 2" which was released on February 14, 2012. She made a cameo appearance on the drama following its release to perform the song.
On July 23, 2014, it was revealed that Ye Eun would be going solo under the pseudonym Ha:tfelt (Meaning Heartfelt/Hotfelt). JYP Entertainment released a teaser for her debut mini album entitled "Me?" set to be released on July 31, 2014. Later that week, a second teaser video was released for the album's title track, "Ain't Nobody", along with several image teasers on her official website. HA:TFELT previously gave a preview of her mini album through her artistic teasers and special exhibition <HA:TFELT's 1st Exhibition 'Me?'> held on the 30th. Now Wonderful were able to get a full listen of the album which consists of 7 tracks composed, written, and arranged by HA:TFELT and collapsedone. Fellow member Lim and Beenzino participated in a featuring for the album, as well as SOOL J who also participated in the rap making.