Sonia G Flat Definer (Keyaki) is a brush.
Sonia G Flat Definer (Keyaki) ($125.00) is a small, flat eye brush that works well for pressing and patting eyeshadow into place with greater precision, particularly for those with smaller features or who need a smaller brush for more detailed work. The version included in this set features undyed saikoho hair, so it seemed slightly more tightly bundled together (seemed a bit narrower than my dyed version) and seemed to retain more of its original shape after washing. I've found that this brush works well for placing product, but I find a pencil brush is more suitable to smudging out eyeshadow or eyeliner.
You can read my original review of the Flat Definer.