In Japan, there is a thing called a monarch. That means there is a person who is the leader of the country but they are not elected by the people like a president is. They are born into the royal family and they become the leader because of that.
However, there are some people in Japan who don't like this system of having a monarch. They think that everyone should have a fair chance to be the leader, not just someone who is born into a special family.
These people are called anti-monarchists. They want the royal family to have less power or for them to not have any power at all. They think that having a monarch is not fair and it goes against the idea of equality.
Some people are against monarchs because they think that they are unnecessary and it costs a lot of money to support them. Others think that the idea of having one family rule the country is outdated and not fitting for the modern era of democracy.
So, in summary, there are some people in Japan who think that having a monarch is not fair and they want to change the system so that everyone has an equal chance to be the leader.