A quiet, hardworking country who is described as dealing with matters as an old businessman would do.
A shy, quiet and hard-working man, Japan doesn't know very much about the outside world and needs time to adjust to other people. But he's very curious and interested in learning things from other nations. His distinct island customs may seem mysterious to others, although he finds them perfectly normal. He tends to have the behavior of an "old man" and was a hikikomori for a long time (Japan had spent about 250 years in isolation keeping only contact with Netherlands). Japan has voiced his preference for 2D girls over 3D girls to England, Greece, and France in one strip, hinting that he has an otaku side. His otaku side is further shown when he decides to buy a Shonen Jump magazine in his preparations for the New Year.
Japan seems to be fond of food in general, very similar to China's fondness, his country's food in particular, as evidenced by his annoyance of having his salted salmon taken off Germany's diet plan. He expressed dismay at the increase of the price of eggs due to a bad economy. He also had the urge to touch the Italy brothers' ahoges due to them reminding him of vegetables. It is said that cockroaches are one of the things that Japan hates the most, to the extent where he could cry over them. Although he appears relatively calm most of the time, it is suggested that his anger would be the "scariest". However, it is shown that it's hard for him to get that angry, as he is mostly able to only summon an "unpleasant feeling".
He has a weakness for soft and fluffy things.
After being discovered by China as a small child, Japan was raised by the older man, who taught him how to use kanji (which Japan used to create the hiragana alphabet). One day, Japan turned against China and attacked him with a katana, leaving a disfiguring scar on China's back. From this point, the two were enemies in war, and China despaired over how war had changed Japan.