Blood prominently appears in the work of SUDA51, however in the video games killer7 and Killer Is Dead it is incorporated directly as a major gameplay element. It is said to help stabilize the multiple personalities that exist within Garcian Smith, allowing better control of them, as well as heightening their powers.
The blood spilled by a Heaven Smile can be absorbed by Harman Smith's personae, and is classified into two different categories: Thin Blood and Thick Blood. However, normal attacks will cause most of the blood to spill uselessly onto the ground; critical hits will allow all of the target's blood to be collected.
The blood gameplay mechanic recurs in Killer Is Dead, in which it powers protagonist Mondo Zappa's healing, sub-weapons and instant-kill attacks.
Thin Blood is collected in test tubes and is used to power the Smiths' special abilities, as well as heal them while in the field.
Thick Blood is collected in a beaker, and is treated like experience points. After accruing enough quantities of Thick Blood, the liquid can be processed by the Mad Doctor through a television in Harman's Room, producing a serum which can upgrade the Smiths' attributes. Upon giving the serum to a member of the Smith Syndicate, their consciousness will heighten, allowing access to their special abilities and attacks, as well as leveling them up.