If you want a cheap flight from Cardiff to Osaka, you've got one airlines to choose from.
You can use the filters on your search to see more flights and find cheaper rates – Osaka has more than one airport. So if you don't need to fly into Osaka Kansai International Airport, it's worth checking your other options. The 9659 km flight usually takes about 18 hrs 35 mins.
If you're planning on going to Osaka during this time, you could take a look at other airport options. Or you could try to get a last-minute bargain.