In this case onigiri means demon-killer (oni-giri), not rice ball (o-nigiri, which literally means pressed/moulded). The large yellow characters behind the racket are 鬼斬, literally demon/devil and to behead/kill.
I love the colours! I hope that's available in Europe soon so I might be able to get my hands on one.
Did you see the posts about it yesterday? I'm pretty sure it was in the "Victor Fan Club" thread. Somebody mentioned a release around the same time as the tk9900