From Season 5 of Ranked Matches, starting on 2022/07/21 16:00 JST, "Class 1" has become the highest class of each rank.
Prior to the update, from Season 1 to Season 4 "Class 1" used to be the lowest class in each rank.
Ranks and classes after change become as follows:
Master (the highest rank)
Ultra: Class 1
Ultra: Class 2
Ultra: Class 3
Ultra: Class 4
Ultra: Class 5
Veteran: Class 1
Veteran: Class 2
Veteran: Class 3
Veteran: Class 4
Veteran: Class 5
Expert: Class 1
Expert: Class 2
Expert: Class 3
Expert: Class 4
Expert: Class 5
Great: Class 1
Great: Class 2
Great: Class 3
Great: Class 4
Beginner: Class 1
Beginner: Class 2
Beginner: Class 3 (the lowest rank)