Four-Player Chess/Common openings/1. h3/1...d6/1...h12/1...l9

Kann Variation, 1...l9
Green blocks the g14-n7 diagonal and prepares to play k8 to block the e14-n5 diagonal to defend the weak m6 square.

Red's responses
Red would like to develop the queen, but then the f2 pawn is hanging. Therefore, Red should address this issue first. The two main moves for Red to consider are e3 and d4 to block Blue's queen. An alternative move is g4, with the idea to develop the bishop to g2. Sometimes the move Bg3 is also played, but that is generally considered dubious.