A 3-1 victory in the home leg should be enough but with temperatures nudging 50 degrees Celsius in Kuwait during the day, Japan can take nothing for granted.
Players were already complaining of the heat, plus the sandy dust whipped up on the wind during training.
"I didn't expect this," midfielder Hiroshi Kiyotake told the Sankei Sports. "My throat and eyes hurt."
"I'm fit and want to play," said Nagai, whose replacement Yuya Osako scored in the first leg. "The competition is pretty fierce but I want to prove worth to the team."
Olympic coach Takashi Sekizuka insisted his side were prepared to avoid a repeat of what Japanese fans and media still refer to as the "Tragedy of Doha".
Sekisuka said: "The mental side will be key. We've never been to the Middle East at this time of year but we will deal with the situation.
"We need to stay attack-minded, be aggressive and take the game to them."
"We gave away a couple of silly goals," he said. "But we scored an away goal, we are at home and we still have a chance to win this tie."
