Germany lost their first 2018 World Cup group match and crashed out in the first round, their earliest exit in over 80 years.
"I have to out myself as a bit of a fan of Japanese football. They are really doing it well," Flick told a news conference on Tuesday.
"We see the quality they have in the Bundesliga with Eintracht Frankfurt's (Daichi) Kamada playing a great season or (Wataru) Endo who is one of the best midfielders in the Bundesliga.
"It is a very big task but we go into the match prepared and look forward to it," he said.
There are eight German-based players in the Japanese squad, seven of whom play in the top Bundesliga division.
Underscoring Japan's improvement on the international stage is the fact that the Asian nation had not played at a World Cup finals until 1998 but have qualified for all six editions since, reaching the round of 16 three times.
"In the past days, we had very good training sessions that set good conditions for the first game," Flick said.
"All great footballing nations have the goal of becoming world champions. That's why you are here. When you have the pressure then it's because you have earned it. We will and must reach our limits."
Germany, four-times world champions who also face Spain and Costa Rica in their group, are desperate to put the 2018 debacle behind them.
One player eager to do so is Joshua Kimmich, who was part of the 2018 team.
"The motivation we have is huge. We know 2018 was nothing and we had to wait four and a half years and what will be important tomorrow is to start with a good game," the versatile midfielder said.
"That is extremely important. At the Euro (in 2021) we lost the first match, at the 2018 World Cup we lost the first match so my focus is on tomorrow and I am convinced we will win."
