Choujuu giga is a jutsu to create sketches which can be used for various purposes. Sai on his roller sketches depict the sketches will be living. If exposed to attacks, sketches of life can disappear and turn into ink.
Sai drawing a tiger which he uses to attack and Fuuka giant spider. Sai drawing birds use to fly the vehicle. Sai use this to exit from the labyrinth of stone Fuuka.
Ink sketches can be lost when exposed to pike gansetsukon Fuuka, or hit something in the high speed.