Japanese school rankings has S above A, where S means 10/10. I believe it stands for Superior, as some countries use some variation of an I-M-S (Inferior, Medium, Superior) grading system. Example: Brazil uses II-MI-MM-MS-SS (so SS kinda means "Superior-Superior").
That's why Japanese games use the S-A-B-C-D scale.
It's not anything new or video-games exclusive, the Yu Yu Hakusho anime, aired from 1990 to 1994, commonly mentioned the Rank A and S monsters are the biggest threat in existence.
Note: those "High Spectations Asian Father" memes are wrong because "A" in Japan is less than excelent.