By mentioning your visit to the World Cup games in Japan, people will instantly know that you are a soccer fan. It will give them some ideas of what you'd like to do or where you'd like to go in relation to the Games.

Before arriving in Japan
Nihon ni sakkaa/Waarudo Kappu o mi ni ikimasu.
I am going to Japan to see the soccer game(s)/World Cup Game(s).

After arriving in Japan
(Nihon ni) sakkaa/Waarudo Kappu o mi ni kimashita.
I came (to Japan) to see the soccer game(s)/World Cup Game(s).

Note!
In Japan, the word football is not used.
Please use sakkaa when you are talking about football.