Ayaka was on the January 9 "R no Housoku" episode dedicated to Little Glee Monster
And even mastered a difficult LGM backing vocal :)

On A!O: https://aidoru-online.org/torrents-details.php?id=102303

January 15
Ebichu [Event] Shiritsu Ebisu Chugaku Shugaku Ryokou

January 18
Aiai [Event] Saki

nico
http://live.nicovideo.jp/watch/lv287884810
open 18:20 start 18:30

"Saki" theme song will be released on February 1
http://natalie.mu/music/news/217348

I'm no expert so I'm only guessing. But in this case it's tied in with the TV show producing the single. So artists having signed for that production may be free to appear on that release by contract and permission.
It will be different for three groups of the same agency working with different labels producing something.

Though in the end I'm sure it's "merely" a financial matter....

I started listening to Ebichu around the graduations of Hirono, Natsu and Mizuki, fell in love instantly and decided to get every major single (and albums), but never went back to their pre Karikeiyaku no cinderella era... long story short i got the album with the babies cover, so here it is for anyone willing to take a ride on the nostalgia train.



https://drive.google.com/drive/folders/0Bx8Tdl0miCP-ZmdGR1NCa3FNeFU?usp=sharing

January 24
Ebichu [TV] Uso no Youna Honto no Shunkan SP
Matsuno Rina
Kashiwagi Hinata
https://video.twimg.com/ext_tw_video/823888226783924224/pu/vid/1280x720/fMKIY4vsghHz63uB.mp4

Mayama Collaborates in the new mini album of Haruna Nana with the song "Purple Love"

http://www.mayamarika.com/artist/mayamarika/info/477741
http://natalie.mu/music/news/218328

instagram
Riko
https://www.instagram.com/nakayama_riko_official/

aiai: Rittan!! I was waiting for it!! Since when aiai started Insta, I thought you will soon lead too! And it's become true!! You have such cool pictures! You approach instagram as icing! Waiting for posts!

Riko: Thank you!

aiai: ahhh she replied to me!!