Sonia G Mini Booster (Keyaki) is a brush.
Sonia G Mini Booster (Keyaki) ($125.00) is a smaller, denser crease brush with a tapered edge. It seemed slightly firmer/less flexible compared to the dyed version in the Sky series, but they both worked well in terms of placing and diffusing color. I'd argue that the undyed saikoho bristles are slightly more precise and may pick up product a bit more heavily but wasn't as diffusing as the dyed version (by a few hairs, ha, ha).
You can read my original review of the Mini Booster.