By focusing. Nearly all of a shade's powers stem from strength of concentration. [Which was good news for Shuichi, as that's one of the things he's best at.] If I picture my body in my mind, I'm able to condense my shadows to the point where I become solid again.

[He gives a vague sort of demonstration with his hands as he speaks, miming "condensing" something between the large, ghostly claws.]

That body doesn't quite...function the way a normal, living human body does, but it is at least corporeal. I look like myself again, and I don't have to rely on telekinesis in order to interact with the world around me. Buuttt...I can only do it in the dark, which is why it's not always an option.

[And why he's not doing it right now. Because then poor Obi-Wan would be sitting in pitch darkness thanks to the blackout curtains. And that would just be poor hospitality.]