Hi.
Well I checked some Japanese sites, and it says PocketDos doesn't support Japanese input.
I assume you're using the Sigmarion 3 with PocketDos in English, but I think the PocketDos doesn't recognize the arrow keys unless you somehow tell it the keyboard type?
The site says English text and numbers are supported in PocketDos, but not Japanese.
What I think is PocketDos can't recognize the special Sigmarion 3 keyboard layout.