Yet another Milgram observation I've had: Most of the prisoners have seen an alternate version of themself at some point in one of their MVs - the only exceptions are Kotoko and Mahiru (I was really hoping it would happen with Kotoko in Deep Cover but I guess not. Perhaps T3?)
Haruka - He sees a younger version of himself in Weakness.
Yuno - She's frolicking with a bunch of Yunos in Tear Drop.
Fuuta - He sees himself walk by to vandalise the graffito in Backdraft.
Muu - Okay so this one is a stretch but bear with me. It's not made explicitly clear, but there's a scene in It's Not My Fault where Muu is laughing with a bunch of her friends when one taps her shoulder to bring her attention to something (something serious, judging by her expression). Muu turns around and then the camera changes to a panning shot of Muu's crime scene. They don't share the same screenspace but I choose to interpret this as Muu seeing her crime from another point of view.
Shidou - He reaches out a hand to another him collapsed onto a bed in Triage.
Kazui - For a large portion of half he's watching himself on stage.
Amane - A lot of Amanes march together during Purge March.
Mikoto - Technically it's Mikoto and John (not just Mikoto seeing himself), but visually is fits in this list. It happens more often in MeMe, but it does happen in Double as well.
Y'all realize that if John is truly a new alter at least one has to have existed before him right? Even if the "third" alter (dubbed Midokoto) is no longer in the system/story, he WAS there.
Mikoto. Was never. A singlet.
Ever.
That's just not how DID works. Mikoto has to have had childhood trauma to have alters; you don't just split from stress in adulthood without ANY parts beforehand.
With this distinct difference in appearance, it's plenty reasonable to argue this guy could be John's predecessor (not John, but also NOT Mikoto).
So yeah it's plenty reasonable to think about the other alter and treat him as a factor in the story, whether or not he's around anymore. Bro is not like "an OC," he didn't come from nowhere. Systems cannot ever be singlets because their brain's development was disrupted; if John is truly new, someone else has to have previously existed alongside Mikoto.
Idk I trust that Yamanaka has thought this stuff out but this is just my opinion lol