I've already explained why Japan fears no human group in the blog thread. Here I'll show how this manifested itself through history.
The first case is in 600AD when Japan tried to help Baekje take back their country from the Silla and Tang Dynasty. The outcome was a failure but, Think about it, Japan sends some 5,000 troops to fight the proto-Korean country and the Chinese empire thinking they could win.
The next time is in the 12 century when Kublai Khan demanded Japan to become a Vassal of the Mongol Empire, but each time a messenger party was sent, they were sent back with no reply. It is reported that one time all but one person was killed and he was sent back to tell the Mongols what had happened. Now, the shogun knew that all of Asia had fallen to the Mongols yet instead of fearing an attack, he set ready for war and even though the Mongols attack, Japan defeated them. The Mongols threatened a second even bigger invasion but Japan did not surrender, instead, they beat back the Mongols a second time.
The third time was in 1590 when Japan decided to conquer China, Yes Conquer the Chinese Empire. Japan asks Korea to be an alias to take China but Korea refuses to reply. So Japan decides to conquer Korea first as a stepping stone to get to China. The combined forces of Korea and China again stop Japan from taking any piece of the mainland but the Japanese did try twice and this did put expend a lot of military assets for the Chinese. This and other causes so weakened the Chinese that the Manchus conquered them some 30 years later. The Manchus didn't dare try and take Japan.
Around the 15~18th century, Europe was taking over all of Asia. Portugal was supposed to colonies Japan but they were not successful. Japan did not fear the Portuguese, were not wowed by their technology nor suckered in by their colonization tricks. Japan instead kicked out the Portuguese and killed all the Christian converts since they were loyal to Christianity which ultimately made them loyal to the Portuguese church - after all, the Portuguese priest knows the will of God, not the Shogun of Japan. Japan tells all foreigners to keep out and none dared to trespass until in the 18th century the Americans show up.
The first time Japan had to respect the might of a foreign power was In 1850 when the American Admiral Perry sailed his gunships into Tokyo bay demanding Japan to open its ports to America. That's like pointing a loaded gun at someone and saying "You should sign on the dotted line or very very very likely bad things might happen to you immediately." lol. Greedy, Underhanded, Evil, Disgusting Americans, possibly. America was and is the most powerful nation ever on the face of this planet. Yet some 30 years later Japan attacks this giant power and bombs the c**p out of their Pearl Harbor Fleet. It took two Nuclear bombs - the only nukes ever to be dropped on humans - to force the Japanese to surrender.
Japan has a history of not fearing anyone, but even more, A history of believing they can fight anyone and win.