Not a technique per say. The Blood Frenzy is a state of being expressed by those capable of performing the Blood Release: even should they receive the release by way of blood transfusion. The Blood Frenzy is one of the many possibly fatal downsides associated with the Kekkei Genkai, but one that can also be managed and put to actual use. Those born into the Sanguis Clan are inherently bloodthirsty. Driven by their own pain and injuries, the more of these a Sanguis Clansmen takes, the greater their strength becomes. This state of being allows them access to strength comparable to the Eight Gates though at the downside of heightened blood-lust and the inability to tell friend from foe. This state also allows the use of powerful Blood Release jutsu, namely Blood Release: Dance of Death.