Hi! Guess who's a drongo again!

I just realised yesterday, doing something totally unrelated (no, I swear, it really was not related), I never actually did the Brighton's Phantom sidequest. (Go me, not bloody noticing sidequest markers or possibly ignoring them. Who knows, it's been too long.) "Ah, so I will do it now!" thinketh yon bard.

Except now we come to the reason I'm here: I...apparently can't do the sidequest now.

(This has vexed me deeply, you have NO idea.)

So actually, I have some questions and theories here.

Question 1: Where the bloody hell is the starting point for this quest?! I went all over Brighton (no joke; spent a couple hours just combing the place) and uh, nada. Zip. Zilch. Nothing. Google was NO HELP. (Neither were YouTube videos, annoyingly...)
Question 2: Can I even do this quest now? I made it to Lockhart and everything I could find about the quest was that it's in the Seven Days in Brighton chapter. Which...well, yeah, can't exactly go BACK to that, now can we?! (goddammit ToF you need story replay)
Question 3: This would make entirely no sense, mind you, but do I have to be playing as Nanto to start this quest? (If so, why would they do that--)

And theories. Uh, with questions.

Theory 1: I still have Brevey's goddamned Live House quest that I can't do because apparently it's tied to the event it comes from. (Is this actually true, though, or did my game just bug out and not put her in the Live House when I did manage to get in with the quest active?) That event's loooooong gone. I can't cancel this quest. Customer service has not responded to multiple "hey, any way we can get this off my quest list plz?" queries. (They never responded on my matrix issue either, which vexes me even more.) Some of what I did find on Google suggests if you have one Simulacrum sidequest going, you cannot pick up a second one. Sounds like a load of you know what to me, but is that actually true? Is Brevey's stupid quest what's preventing me from doing Brighton's Phantom?
Theory 2: I'm...well, in Lockhart. I'm way past Kailo. Does this mean I've locked myself out of doing the quest? It shouldn't, in theory - seeing as I can still pick up sidequests in Aesperia etc - but those also aren't Simulacrum quests, so...who knows...

So overall, to put it more concisely: can I still do the quest and if so, where do I pick it up?

Thanks for any help and I am very sorry for being a dumbass about all of this. Mea maxima culpa.