For this next game I had Black in SP388 QBBRNNKR. The Queen is in the corner and the three diagonal pieces on adjacent files are aimed at the enemy King, While it might be advisable to get the King away from their influence by castling O-O-O, this is probably not going to happen. Opening the diagonals means moving Pawns, which means the Queenside will be too loose for the King.
The first moves of the game were 1.d4 d5 2.b3 c6 3.c4 Nf6 4.cxd5 cxd5 5.Ba3 Bd6 6.Bxd6 Rxd6 7.Ne3 Ne6 8.Nd3 O-O 9.O-O, leading to the position in the top diagram. After both players have castled, a chess960 game often starts to look like a position that could have arisen in traditional chess, and that is the case here. While I wasn't entirely comfortable with my position -- the pieces, especially the Rook, are not well coordinated -- I didn't feel that I was in any particular danger. My next few moves would be spent developing the rest of my pieces and coordinating them into some sort of a plan.
White has an awkward threat in Ne3-f5, so I played 9...g6, planning to reposition the Knight via g7, thereby opening the diagonal for the Bishop on c8. White played 10.f4, a move which I had underestimated. The hole on e4 is not really useful for Black, while White is planning to operate on the f-file with the possibility of switching a Rook to the h-file to support an attack on the King.
The game continued 10...Bd7 11.Ne5 Qd8 12.Qb2 Ng7 13.g4, leading to the bottom diagram.
Now I started to feel really uncomfortable. With every move White is building a Kingside attack, while Black has not yet latched on to a real plan. More pseudo-active moves for Black followed -- 13...Bc6 14.f5 Nd7 15.Qd2 Qb6 -- but after 16.Nf3, how does Black continue? I felt that my position was teetering on disaster and engine analysis confirmed it. White continued to whip up a terrific attack, I played on in an increasingly hopeless position, and finally resigned well after I should have.
Going back to the top diagram, I still can't find a better plan for Black. If that position is bad for Black, then I must have made a mistake in the moves preceding castling. But where? Was it a general problem of not finding an effective plan earlier in the game? If so, how to avoid this in the future? I'm afraid that there's something here that I'm not understanding.