To get D-class, the player needs to get 50M total power, which is 50 times more than E-class.
After getting D-class*, the player can press the space button twice to fly.
*The quest is to get D-class, 500Million psychic and 100Thousand speed.
When the player reaches D-class, all stats reset, but the stats multiplier is increased by 2 (x2 to x4) and the tokens multiplier by 1 (x2 to x3) which gives the player 75 tokens/minute.
Aura: When the player reaches D-class, the aura has these colors: Red (Arms) and Yellow (Body).
Trivia: About 15.12M players have played the game, but only 1.79M (8.41%) have made it to D-class. (On 19 March 2021)
Check F-Class to have a reference on how to work on this page.