More so than Croatia, the 'wall of the best 16' could be the biggest obstacle in the way of Japan making FIFA World Cup history

Having qualified for back-to-back knockout-round appearances at the FIFA World Cup for the first time ever, Japan have now set their sights of securing a maiden quarterfinal berth at Qatar 2022. Maja Hitij - FIFA/FIFA via Getty Images

DOHA, Qatar -- The round of 16 at the FIFA World Cup is not unfamiliar territory for Japan.

In five previous editions of the tournament, they have gotten this far on three occasions -- and as recently as in 2018.

The next step, however, is unchartered ground. And that is what is making the Samurai Blue's last-16 tie at Qatar 2022 on Monday all the more intriguing.

Physically, it is an imposing Croatia outfit that stand in their way.

As runners-up of the tournament back in 2018 and boasting stellar names such as 2018 Ballon d'Or winner Luka Modric, Ivan Perisic and Mateo Kovacic, Croatia have to be regarded as genuine contenders.

While Zlatko Dalic's charges did not exactly fire on all cylinders in the group stage, with their only win a 4-1 triumph over Canada in which they conceded the opener after just 67 seconds, they have proven to be a tough team to break down.

Along with 0-0 draws against Morocco and Belgium, the Croatians have conceded just one goal so far in the tournament and the result against the latter illustrated their ability to grind out whatever result they needed to get the job done and advance to the knockout round.

Croatia will head into the tie as favourites. That is for certain and it probably will not bother Japan that much.

After all, they were also underdogs in their sensational group-stage wins over Germany and Spain.

Perhaps the bigger obstacle to the Samurai Blue making history and reaching the last eight is not the opposition physically squaring up to them, but the doubts -- even demons -- lurking in their minds.

Mentally, the greatest test could be overcoming what Japan defender Yuto Nagatomo has called "the wall of the best 16".

An intangible barrier that every previous generation has failed to overcome, even when they have boasted icons like Hidetoshi Nakata, Shunsuke Nakamura and Keisuke Honda.

Speaking at Sunday's pre-match news conference, Nagatomo called on his teammates to harness the spirit of the Samurai and show the courage necessary to make the most of the weapons they possess.

But it was a tweet from earlier in the day from the fullback -- poignant and poetic but a war cry at the same time -- that best summed up the internal battle the Japanese are up against.

"The wall of the best 16. A wall that has stood in the way of Japanese football and my football life," wrote Nagatomo.

"How much blood, sweat tears have been shed to overcome this wall? It's time to break down the walls that have been torturing -- and driving -- us.

"Be brave. Let us all see the new scenery."

The new scenery Nagatomo was referring to? The view from the quarterfinals of the World Cup for the first time ever.

First, there are a couple of obstacles they must overcome. Croatia, and arguably more importantly, the "wall of the best 16".