Originating as a rehearsal group for the residential Sendai Stardust girls, they formed in August of 2015, and loosely participated in different events for the major Stardust idols alongside other regional rehearsal groups. They added the Nidaime when Karen was added in 2015, and removed it in the fall of 2016. At the beginning of 2017, they participated in the event "Ore no Next Girls~Mochiron Fujii~Naruhodo Club eX" in competition with the other small-time Stardust idol units (3BJr, Sakura Ebi~s, regional rehearsal groups, etc.). They came in first place by audience vote, and were given the opportunity to perform with some of the big-time Stardust idols at Stellar Ball. After this point, they started a faux feud with trainee group Sakura Ebi~s, doing joint lives together, and they released a joint song, "Mugen Kageki." They also began selling CDs of their first original songs, "Tenka Ippin~Michinoku Kakumei~" and "Wonderful Touhoku" at live events. They appeared at TIF for the first time last year, and will be there again this year, as well as several other idol festivals, and will continue doing solo events, doing joint events with Sakura Ebi~s, and participating as support for bigger Stardust idols.
They often split up when they make appearances in different parts of the country, so you won't always see 9 (or 8) members all at the same performance. They also have more generations on reserve back in Sendai (Sandaime and Yondaime), although at this point it is unclear if they will add them to the group eventually or if they will just keep them as permanent training groups as they push the main group to become a more formal Stardust idol unit.
Members
There are no individual profile pictures for the group, unfortunately, so these are direct from their Stardust Promotions talent profiles.
Tachibana Karen (橘花怜)
Leader
Color: Pink
Birthday: 2003.10.21
Former member and center of SCK Girls, post-Rikako, previous winner of the Idol Bishoujo Senbatsu. Scouted by Stardust Sendai in 2015, joined Touhoku San shortly thereafter as the third set of additions. Diehard Sasaki Ayaka (Momoiro Clover Z) fan.
Hadzuki Yuna (葉月結菜)
Sub-leader
Color: Blue
Birthday: 2002.09.15
Original member.
Ritsuki Hikaru (律月ひかる)
Color: Pure white
Birthday: 2001.07.31
Original member.
Minato Risa (湊梨紗)
Color: Green
Birthday: 2001.09.02
Original member, but currently on a sort of hiatus. Still blogs occasionally, but doesn't usually participate in any events nowadays.
Kitami Rine (北美梨寧)
Color: Purple
Birthday: 2002.05.28
Original member.
Yasumori Waka (安杜羽加)
Color: Yellow
Birthday: 2002.10.30
Original member. Winner of the Touhoku Dream Audition 2016.
Sakura Hinano (桜ひなの)
Color: Orange
Birthday: 2004.05.06
Part of the second round of additions to the group, along with Date Kahya. Diehard Ebichu fan, particularly of Kashiwagi Hinata.
Fujitani Miu (藤谷美海)
Color: Light blue
Birthday: 2005.03.09
Last addition to the group. Glasses.
Date Kahya (伊達花彩)
Color: Red
Birthday: 2005.03.21
Part of the second round of additions to the group, along with Sakura Hinano. Formerly went by just "Kahya."
The colors don't mean too much currently, or at least not as much as they do in other Stardust groups. When asked about official colors before announcing them, they said that they were more focused on the name bibs rather than the colors, and they do wear bibs for most every appearance so they're a bit easier to recognize by name.
Mugen Kageki MV
Tenka Ippin Live
Ordinarily I would wait until a group gets a debut before starting a thread, but these girls have an awful lot of hype around them right now, even though they're still not really considered part of the Section 3 Idol group yet. In any case, this will give people a place to learn about them and hopefully keep up with their activities.
Stardust profile (no official website yet)
Official Twitter
Official Blog
Former blog (shared by all local rehearsal units)
Stardust Sendai Twitter (previously used for all news regarding the group; nowadays it's only really for the male idols, but if you go back far enough you can find some old media related to the group)
There is also a very dedicated fan who uploads tons of videos here, collected from Twitter, livestreams, TV, etc.