I just came accross the group Kotakura. I clicked on a video of them because I thought it's Takuya Matsuoka in it and you know what, it's actuelly him (middle). It seems like he is in this group as well as being an solo artists. The other two members are Shousei (right side) and Naoki (left side). Shosei and Naoki are also active as the duo "crossover & co." (former named "Collagen BOY'z"). However Kotaku is still active.
It seems that "Collagen BOY'z" were the opening act for Matsuokas 2014 tour and around that time they became very good friends and spontaniously decieded to form the group "Kotakura". So they are still active in their main group / solo but also with Kotakura. Since all of them have other activities Kotakura is not very active but they already released three albums which is a good thing. Their voices harmonize very well. Here are some of their songs.
The first one is my favorite it's extremly beautiful. If you want to know about the other group as well tell me, I will try to find out more about them.
What do you think about them?