K-Pop is a fast-paced genre where the best song is always the newest one. Songs that were popular a few months ago have faded away to make way for the newest chart toppers. There are some exceptions, but K-Pop in general is always moving forward, trying to find the new catch that will hook the fan's attention. Toheart, a collaboration duo made up of SHINee's Key and INFINITE's Woohyun, may very well be the start of a trend for inter-group collaboration units.

Toheart is not the first inter-group collaboration. Recent inter-group collaborations include BEAST's Hyunseung and 4Minute's HyunA's duo Trouble Maker and M&D, made up of Super Junior's Heechul and The TRAX's Jungmo.

For whatever reason, while those two groups gained some attention, but neither of them spawned talk of further collaborations between other artists.

However, Toheart has seemed to open up a conversation in K-Pop about more idol collaborations. In general, idols occasionally feature on one another's songs, but it is rare for there to be any sort of formal promotions, let alone the creation of a new unit. The fact that members of SHINee and INFINITE were able to come together to create a new unit and promote together reveals that there is a chance for collaboration units to be successful. 

Subunits within idol groups have been the general trend for several years, but Toheart's example seems to have some other idols thinking.

The show Entertainment Weekly spoke to Noh Junyeong, a music critic journalist, about why duets in general are popular and he explained that "if singers from other groups or solo artists collaborate, they can use their strengths to perform for bigger goals." This can help them become more successful. 

MBLAQ recently appeared on the popular show Yoo Hee-Yeol's Sketchbook, and they discussed the artists that they would like to collaborate with. Rather than being just simple duets, as many idol collaborations are, the conversation was about what other idols members of MBLAQ wanted to promote with as a unit.

This distinction is interesting, because until recently there was no real thought of idols collaborating with idols from other groups, let alone different companies. However, Toheart's recent popularity may have drawn enough attention to the potential success of inter-group units.

While the idea may have seemed just like something out of fan's dreams a few years ago, the attention that Toheart and Trouble Maker have received has led to inter-group units being more accepted.

While sub-units from groups and temporary collaborations are still very popular, it will be interesting to see in upcoming days if other idols come together to create new promotional units.