Boots with a pliable upper intended to be folded down, usually to display a contrasting color, pattern, fabric, or other embellishment inside.
Hololive character designers have an inexplicable affinity for them.
Hoshimachi Suisei post #3931913
Houshou Marine post #3589684
Natsuiro Matsuri post #3310397
Shirakami Fubuki post #3159364
Tokino Sora post #3731846
Uruha Rushia post #3571510
Yozora Mel post #3931919