savename <character string 1>,<character string 2>,<character string 3>

Designates the names for savefiles.
From left to right, the strings are: the title string for the save menu, the title string for the load menu, and then the name of the save itself.
By default, these are "<セーブ>","<ロード>","しおり" -- note that these are all 2-byte character strings.
It follows that this function will only take 2-byte character strings as input.