Toheart

In January 2014, following the merger of Woollim and SM in August 2013, it was confirmed that Key and Woohyun was currently recording for a collaboration, with the album to be out as early as February or as late as April. On February 20, a prologue video was then released, revealing that the unit's name would be Toheart. On March 3, they debuted with the release of their mini album, 1st Mini Album.

On April 7, they then released their first digital single "Tell Me Why", which included a broadcasting and acoustic version of the song in the first mini album. The duo then proceeded to disband in 2014.