I'm happy to see this topic kind of coming to life again, and it's interesting to have someone else here who has seen the butterflies. Vanmonky's description fits with most of the others, so I think by now we can assume that if this butterfly event exists, it takes places rather late in the game.
On that note, I tried some of the things I suggested in my previous post, since I coincidentally still had a save file in Hour VIII. In that file, I already had the Standing Girl and Seated Twins photos, so I just tried waking up and talking to Miku a couple of times. Unfortunately, she doesn't give you the information from her photo research until after the end of Hour VIII, so this is already different from what I experienced withe the Crawling Woman events. I didn't find the butterfly after getting the info from Miku in the next Hour, which didn't really surprise me in that case.
Now, I guess playing through that entire Hour again and trying different versions of what you could do there would be next, but I'm inclined to believe the trigger either isn't there or has some other requirement. Which brings me to something midwinter and I discussed here years ago....:
The encounter with Yoshino is definitely after she's already died. It happens immediately after the first fight with Yoshino and the Black Shadows, and Yoshino isn't an attacking ghost until she's turned to ash. In FF3 they do seem to be quite careful about showing the difference between living people and ghosts, so if Mio did start appearing in other places that would be pretty weird. So I'm inclined to think it didn't happen, but who even knows at this point?
This got me thinking again. If you don't save Kei, you also don't save Mio, right? What if we need to look at Hour X, where Kei's ending is determined, then? I said before that we might need to be on the path to a specific ending, and this actually makes it even more likely. If Mio really does appear as part of the butterfly event, it can only happen if we're on the path to Kei's bad ending. It wouldn't make any sense otherwise. So, that would be my next attempt at solving this, I think. Play up to that point and then, once I'm on the path to the bad ending, keep waking up after pretty much every little thing I do. It's also possible that this takes place a bit later, after Kei's death, IMO. Doesn't make it any easier to find^^"
Of course, this is assuming that everyone who believes to have seen Mio there did NOT confuse her with Mayu in the heat of the moment. There's a real possibility that the ghost seen after following the butterfly is Mayu, which would mean we can't take it as a time indicator at all, of course. But I'd suggest assuming it really is Mio for now and trying things out based on that.
EDIT: Actually...you can't get the good ending on your first playthrough, can you? That would be even more evidence for it playing a role, since most players who saw the butterflies reported doing so on their first playthrough, which means they were on the path to Kei's bad ending by default.
Edited by Dark_Shiva144, 29 October 2019 - 12:21 PM.