6th Generation; 22 Sai no Watashi

[PikkoroZoro]

(o￣∇￣o)(ノ≧Ｏ≦)ノ　ダメ～～！

[GingerOreo]

It's because Miki didn't come out from the same competition as the three of them. Miki was more like a 4th gen member (supposedly to be) because she was in a similar contest with the 4th gen members at that time but didn't get in. By 6th gen then they decided to add Miki into Momusu which is why you don't really see Miki mixing with 6th gen much and she was often seemed more senior than the 5th gen even though she's of a later gen.