I agree with the assessment that it is a Queen. But it doesn't seem to make much difference unless it does. The only "good" suggestion for what the anomalous feature is under the melting queen is "rabbit tail ". Yari-Shogi has a 7x9 board but Tori Shogi has a 7x7 board and uses the phoenix and other birds as pieces. If it were a QR code somehow, one would have to make it a square first which would involve cutting two columns (non rotated view) off the board. If you cut the right most two off, you frame the "white rabbit" nicely.

Very nice and thorough synopsis of leads crax0r! I'll be coming back to that post often.