The Asian champions let a lead slip in their 2-1 defeat to Ivory Coast on Saturday, a result that leaves them playing catch-up in Group C.
A crucial clash against Greece looms large after Fernando Santos' side were beaten 3-0 by Colombia in their opening fixture.
And Kawashima claims the Japan squad is still full of belief ahead of Thursday's match in Natal.
"It's important that we have to be fresh for the next game," Kawashima said.
"We have to change our minds for the next game. We just have to give 100 per cent to win the game.
"We have a good group and we have confidence as well so we can't lose our next game.
"We believe in ourselves."
Japan entered the World Cup on the back of a five-match winning streak, including a 3-2 triumph against Belgium last year.
