It'd be nice to have the option to move characters with two clicks instead of click-and-drag as that's rather uncomfortable on a laptop touchpad.
Maybe let you right-click on a single enemy to keep their movement/threat displayed while you move your own pieces.
It would also be nice to display an X or something on spaces that Kings can't move onto due to threat instead of just leaving them empty. (also, an indicator for being in Check)
And a final question: why no Rooks?