It's the staircase in the woods again. You know the one. Mysterious, abandoned, the one everyone says you shouldn't climb. Well—maybe if you did, everything would be different. Maybe you would become something else entirely. Something you've always feared you secretly already were.
Matt should not be played by someone who is cis; he is a nonbinary transmasc person early in transition. Harriet and Isabel may be played by cis or trans men. (If you want to get granular about it, Isabel is likely trans, and Harriet can be either cis or trans. But the impression/vibe they project is "man"—however achieved.)
Matt and Harriet should be played by Asian performers; Isabel can be any race but please don't default to casting white performers because I said that.