Whirlwind lets Amaterasu and Chibiterasu create a tornado around them that will blow all their enemies away. Whirlwind can also be used as defensive, and also to put off flames with the same usage as Galestorm.
To use Whirlwind, draw three horizontal lines on the Celestial Brush's canvas.
First, Amaterasu needs to purchase a Marlin Rod for ¥10,000 at either North Ryoshima Coast or Sei'an. Then, on an island at North Ryoshima, fish a Marlin, then go to Umi's restaurant on the beach. In the kitchen, as Umi prepares and slice the fish, draw 3 horizontal lines. Kazegami then grants Amaterasu Whirlwind.
Chibiterasu can purchase Whirlwind for ¥50000 from the shaman at Yakushi Village after 9 people have moved in.
Spoilers end here.
When Whirlwind is used, the kanji 風 (kaze, wind) appears.