If you want a cheap flight from Bangkok to Tokyo, you've got zero airlines to choose from.
Tokyo Haneda International Airport is just one of the airports in Tokyo. If you're not set on a specific airport, try changing your search from Tokyo Haneda International Airport to Tokyo to see a broader range of flights – they might be cheaper.
You can expect accommodation prices to be higher at this time of year too. Last-minute deals do crop up, but it's best to book everything in advance to avoid disappointment.