The Strife Specibus fistkind is used by a few characters in Homestuck, most notably by Equius Zahhak. As the name suggests it involves the user attacking with their fists, though why one would need a strife specibus to wield their own fists is unclear.
Roxy Lalonde is also with a fistkind specibus in their Strife Portfolio, and they are seen using it during Collide. Their pre-scratch counterpart in was seen beating an enormous monster from LOLAR with only their fists as well.
Many players have been shown punching enemies and other players without Fistkind, so it can be assumed that this specibus amplifies the user's hand to hand ability.