Kirk here with a little illustration I made up after I read Fiona’s post, which is here, by way:
https://www.facebook.com/Kumamotoi/posts/7092504690822902
I hadn’t heard of dekopon being called “Sumo oranges” but I was aware that they are also known as Shiranui. Wikipedia says that “Shiranui (不知火, unknown fire, Shiranuhi in the historical kana orthography) is an atmospheric ghost light” that appears in the Ariake Sea off Yatsushiro at certain times of the year.
I thought that “Sumo orange” might make a cute character so I did an image search but didn’t find anything. Hence, my do-it-yourself version. :)