I came here in autumn and to be blunt it was pretty lame.
Yes beaches are 100% better in summer. I can get that.
Perhaps as an Australian I have been spoiled in regards to beaches.
But, if you come here in Autumn, and also probably winter. It will be cold, and windy, and boring.
Your best bet, is to walk back up the road into town, and grab a killer burrito and beer from some glass building on the main road. Somewhere around 1000 Yen for the two.
Then you can sit there, enjoy your burrito, and your beer, and forget this beach exists.