Another differentiator between SideM and all of the other imases that came before it is the very strict adherence to units. Everyone belongs to a unit and they are bound for life to it. Now, that’s not to say that there aren’t situations where everyone breaks out and mixes together, but you’ll notice, for example, whenever seiyuu or characters do their introductions, that they don’t only give their name, but also the unit they belong to.
Even now, I’m not entirely sure how I feel about the strong organization around units. I think it’s worked out so that it’s helpful for quickly establishing relationships, since there are so many characters, but it can feel a bit constraining at times. In most of the mobage events, units tend to stick together, so there are limited opportunities to for characters to interact outside of their units.
More practically speaking, this also means that music is organized around the units. This is less of a problem in the other imases, since group songs usually aren’t strictly “owned” by any one group. In SideM, the songs so far are very heavily based in the units’ identity because they also serve the purpose of being an image song for the unit.
The Origin@l Pieces series is a start to the giving each character a bit more of an identity outside of their units. The main attraction is obviously each character getting their own solo song, but the events gave the characters more of a chance to spend some time with each other outside of their units, which was kind of nice. It should be noted that while the stories in the mobage are still fairly heavily unit-based (save for a few special occasions), LIVE ON ST@GE!! seems to be dealing exclusively with events that aren’t unit based at all (possibly because of the gacha/reward structure).
An interesting question will be to see how far away from the unit concept SideM will go. For the moment, it seems like OP was a diversion rather than a new direction that they want to explore. All of the new music, whether it’s the Animation Project series or the 3rd Anniversary Disc series or the Starry Collaboration series, is entirely unit based. It makes me wonder if we’ll ever see full-length performances of any of the solos at the lives, since even during the Greeting Tour, they were only willing to perform short versions.
In the short term, this doesn’t really seem to make much of a practical difference, but I can see the unit structure causing some practical problems in the future. We can already see some consequences in the 3rd live tour, where Jupiter, Beit, and Sai are confirmed to be performing at only one of eight performances. In the case of other imases, having others fill in is not such a big deal, but again, unit identity is much more important in SideM. It’s something I’ve been thinking about since the start and it doesn’t seem like there have been any good solutions so far, but we’ll see.