Alberto Zaccheroni's side are facing an uphill battle to reach the last 16 after Ivory Coast came from behind to beat them 2-1 on Saturday.
Greece also enter Thursday's Group C clash on the back of a loss after they were put to the sword by Colombia 3-0, raising the stakes.
Okazaki felt his side veered away from their usual style of play after taking an early lead against Ivory Coast thanks to Keisuke Honda's stunning goal.
Okazaki said: "We had an aim to play with our (aggressive) style from the start in this World Cup, but when we scored the goal in the first game, the consciousness to defend disturbed our mind.
"We became a little wary as it is the World Cup and because we wanted a win.
"It is most important to play more aggressive and not to be too defensive, staying in the back (half) like we were in the last game.
"All we have to do is just to show our abilities. I have an image to go forward aggressively against Greece in my mind."
The forward did not manage a shot in anger against the Ivorians though and said he was focused on "pouring my energy into the defence".
Mitroglou - Greece's top scorer in qualifying – has battled knee injuries throughout 2014 but came off the bench in the second half of their Colombia loss.
"We watched them play against Ivory Coast," he said.
"We selected interesting information and we will inform our players. We have already watched Japan in the past and we know their advantages and disadvantages. We will be ready."
