Hm... as much as I liked this theory, now that I keep thinking about ep 4 it seems like there's a flaw with this:

Wataru doesn't seem to know WHO Yuuto's old band was

He does have a reaction toward GYROAXIA, but doesn't show as much worry or concern as Yuuto does https://twitter.com/lovemailforargo/status/1256423809609015296

Now what I'm thinking about that screenshot is Nayuta bursts into their practice session and he and Yuuto talk shit to each other.

I keep thinking about these factors:
Wataru and Kenta haven't been in contact for a while
Kenta has a different last name than Wataru
Yuuto didn't recognize Mashu, meaning Yuuto's possible involvement was at a time when GYROAXIA wasn't pro

Because Wataru and Kenta weren't in contact, he would have no way of knowing Yuuto had ever been involved with GYROAXIA
Because Kenta and Wataru have different last names it never occurred to Yuuto that Wataru would have any sort of connection to his old band and kept it secret

The one big question that remains is, where did this all take place? Was Yuuto in Sapporo for a brief period of time?

Also, how much of the old GYROAXIA remains? Is it just Nayuta? Was Kenta even a part of GYROAXIA when Yuuto was there?

And how does Reon fit into all of this?