This pose involves up-and-down and back-and-forth both the movements so that she can enjoy to the extreme rubbing her groin against his groin.
Steps to perform:
Step 1: He sits on the chair keeping a fair gap between his legs.
Step 2: She sits on his groin to rub and grind.
Step 3: She holds him through his neck and he grabs her by her waist.
Step 4: Now she initiates the action rubbing her groin against him.