Highlighted: where the king and rook start and land.
Weirdest castling #8
SP-3 · bqnnrkrb
O-O · K f1→g1 · R g1→f1
90 of the 960 starts castle exactly this way.
Destinations are fixed in Chess960 (kingside K→g1 R→f1, queenside K→c1 R→d1); only the starting squares differ.