Sooner or later, groups disband. It's the sad truth. In the early years of Kpop, groups would suffer from the 5-year-curse, which meant that once a group hit 5 years together, chances of them breaking up increased severely. Examples are H.O.T (1996-2001) and S.E.S (1997-2002), who both lasted exactly for 5 years before splitting up. Nowadays, this curse seems to have somewhat vanished, with groups like Big Bang, Super Junior, SNSD and SHINee having stuck together for way over 5 years and are still going strong. And of course, who could forget Shinhwa?
However, as a group approaches the 5 year mark (or even earlier), most members have their own individual activities and the group only comes together for the annual comeback and the year-end shows, so it's not so strange that maybe one or two members will release solo material, or even form a sub-unit.
Those who appeal to another market
Super Junior is one of the earliest groups to try this concept, having to this day (I think) 5 different sub-units. There's the trot one and the "happy" one, both of whom are inactive at this day, but Super Junior-M released new material very recently. One of the more successful Suju units, I would say, having a reasonably large fanbase in their targeted country China. Currently it possesses two Chinese speaking members- Zhoumi and Henry, whom the latter also has gone solo.
Appealing to a different market is a great way to promote a sub-unit, and this is what Super Junior has done with all of theirs. Apart from having a Chinese unit, they also have the vocal trio of K.R.Y (whose rendition of Sorry Sorry still gives me the best kind of goosebumps) and best friends Donghae & Eunhyuk who recently released a Japanese album.
Labelmates EXO's original concept, the factor that made them different, was that the group was already put into two units and that's how they also debuted. There was one group aiming for Korea and one for China, and so they promoted up until last year. They released the exact same material, but in different languages, basically.
I would have to mention two other sub-units who have also tried another musical style and promoted to another market than their respective original groups; Infinite-H and Orange Caramel.
Both have very distinct sounds that differ quite a lot from their group's, like with Infinite-H's hip hop concept that is vastly different from Infinite's clean cut, electronic sound. I personally loved this unit, because I love members Hoya and Dongwoo, and it was nice to see them do something that fits them so well, both being dancers and rappers. Furthermore, Orange Caramel has got to be one of the best sub-units that is out there at the moment, and I would like to think they started this whole unit-craze back in 2010 with Magic Girl. Some people loved it, some hated it, but no one can deny that it received a lot of attention. It was original, unique and refreshing, and they have only continued with even more awesome, funny and quirky songs and videos.
Those who do not appeal to a new market
This is the category for the sub-units that exist for other reasons than an exploration of new sounds and styles. It could for example be in order to gain more popularity, please fans or just for companies to make more money. I don't complain, absolutely not, but this is also where the less interesting units come in.
Girls' Generation had no Korean promotions in 2012, much to fans disappointment, so what does SM decide to do? Create a sub-unit to stimulate the cravings as well as cashing in some money at the same time! Everyone wins, right? Well, not my wallet, but otherwise, yes.
TTS, consisting of vocalists Taeyeon, Seohyun and Tiffany formed the first ever SNSD unit, and I suppose it was because they are the main vocalists of the group that they were chosen. I loved Twinkle, both the song and video but it didn't feel like it emphasized on their vocal abilities as much as it did the concept and costumes. It felt like something the entire group could have pulled off just as good, and it made the purpose of the unit disappear a bit. I also didn't like that it was like an EXO commercial, basically, with 4 out of the 6 members of the K-unit making an appearance.
Also in this category we find Sistar19, which was and still is a goldmine for their company Starship. Putting the two most popular members together, having one great vocalist and one known visual, was bound to be a success- and so it was. Ma Boy was huge, as well as Gone Not Around Any Longer last year. This unit too, is even more similar to the original group, with the sound and general concept being exactly the same.
Although, I do think this unit really helped giving the group a lot more public recognition back in the day, along with Hyorin's run on Immortal Song 2.
Those who cross borders
In this category, there are two examples who stick out. First there would be the co-ed duo Troublemaker, made up of Cube labelmates Hyuna and Hyunseung of 4Minute and Beast respectively. The pairing made big headlines with their debut effort, sharing the same name as the project group, and it really shocked a lot of people with its blunt and straightforward sexual approach and provocative dance moves. I personally really like the song a lot, and while the video was a bit too cliche for my liking, it certainly served its purpose. The duo made a comeback last year with Now, and went under the fire yet again for the same reasons as their debut release. I both liked and disliked this comeback. At one hand I liked their maturing image and teamwork, and their concept felt more suitable for their ages, but the song was not as strong as it could have been.
The next unit that has in some ways been a bit of a ground breaker is Toheart, a newly formed duo consisting of two best friends whose companies have been keeping them apart up until just recently. I've written more about their debut single in this post, but their collaboration has definitely made some heads turn. It's not uncommon for artists of different groups to collaborate; sometimes a singer would feature on a rapper's song and vice versa, but this usually applies to idols or artists who release solo material. It's also not uncommon for labels to have their groups interact and feature on each other's songs, but having two members of two separate groups coming from different labels (well, kind of) actually form a group? That's not very common.
As you can see, there are quite a few sub-units here and there, and it's not slowing down for sure. Apart from the ones mentioned above, you can find a sub-unit in almost any group nowadays. It sort of comes along with the formation of a group, that is must have some kind of internal unit. Even some rookie groups have split up into units, for reasons I do not fully understand, but I guess anything goes if they're trying to gain more attention.
For the next part I will be talking about solo efforts by members of groups, and how they can both be a good thing and a bad thing.