Pyriel is right, the emulator is Bizhawk. And the bios is PSP660, that might matter if using my script.
Edit so I don't double post:
Tomm88 figured out that to be able to interact with an invisible character the characters in the slots before them need to be on screen. Not sure if this is universally true, but from my testing it appears to be true in the castle at least. Sonya is actually available much earlier, as long as everyone in slots 0-6 in the basement is in the room and the flag at
is set. Sadly, Crowley hangs out in the basement so you'd need to get him which means CL4 requirement. Also, Krin is forced into your party for Moravia so she's unavailable then too.
It also explains why invisible Moose isn't available without Maas and Meese recruited, the first 5 slots on that floor go Maas, Meese, Moose, Mose, Mace.
Sadly it limits the amount of exploitable rooms quite a bit, as lots of rooms have a late game character in an early slot.
And last thing, technically invisible washed up Kirkis at the dock is possible and interactable. I couldn't find any character to set it up, and your options are fairly limited for characters at that point. I edited his coords though and went through, you can essentially skip the Kouan segment and play up to talking to Mathiu before Kimberly. One of the side effects was the castle not upgrading to LVL2, which makes the Mathiu prompt after Luikan's Hermitage inaccessible.