Currently impossible, requires a magic spray that isn't fire, ice, or light. No such spray exists in either public nor patreon extended demo.
thegodofsky
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Find and kill the ghost lady (which you must have already done to enter nekomata form) and hold down and space bar. That will allow you to phase for a few seconds. To the bottom right of the ghost lady's room is some metal bars, so long as you are phased you can go through those.
You can see it in the picture of the ghost lady in the preview pics.
there are 3 ways to beat her, the Katana, the fireballs, and the protection charm that will allow all your other weapons to hit her. she has a LOT of health so I found it safest to just use the katana in a jump attack-basic combo-jump slide away
I beat her just outside the katana room but I couldn't access it without her killing me. Luckily I found her to the left of her room at the top of the building