If you want a cheap flight from Lisbon to Tokyo, you've got zero airlines to choose from.
New Tokyo International Airport is just one of the airports in Tokyo. If you're not set on a specific airport, try changing your search from New Tokyo International Airport to Tokyo to see a broader range of flights – they might be cheaper.
If you're planning on going to Tokyo during this time, you could take a look at other airport options. Or you could try to get a last-minute bargain.