Costume features in episode: 24
Costume features in Chapter: N/A
This costume is worn in the Little episode and it matches Sakura's Alice in Wonderland costume. The costume is pretty basic in that it is a red top hat with a blue rim. It also has a piece of blue string, which attaches the hat to Kero’s head.
Given the outfit of Sakura's that it goes with, his outfit is most likely a reference to the Mad Hatter, a character from Alice and Wonderland.