The Blood stone (Kor. 블러드 스톤) is an extremely powerful artifact in the form of a crimson crystal. It was created from countless desires, accumulated over a long period of time. One of its special powers is that it lures anyone who knows of its existence. Anyone can grow a longing to possess it. Since the allure of the stone is almost unavoidable, the blood stone was given to Raizel who is remarkably nonchalant regarding powers, to seal it away inside his mansion so that no one else could know of its existence. Its other deadly effect is that it drives its owners into insane beings ceaselessly craving for more power.
Rai kept the crystal sealed away within a chamber inside his mansion, hidden from the eyes of all other nobles. However, after Rai finds his mansion destroyed (during the invasion of Lukedonia) he is shocked to see that the stone under his protection has gone missing. Later on it is revealed that it was Lagus Tradio who stole the Blood Stone. Lagus planned to study it with more time before using it but is forced to use it immediately after finding that Rai has gotten his powers restored.
Gejutel K. Landegre states that the Blood Stone is a cursed artifact that should never see the light of day. He further states that the artifact claimed the lives of so many nobles in the past and Raizel was forced to kill his own brother(older) in an unknown past. Erga Kenesis Di Raskreia also seems to recognize the Blood Stone. Chapter 396 reveals that the Blood Stone caused a horrific civil war in Lukedonia in days long past.
Lagus Tradio created copies of the Blood Stone; one of which is given to Gradeus. The copies are not as powerful as the original but is somewhat similar. Lagus admitted that he had done countless experiments and succeeded in making only a few copies.
In the Noblesse spin-off, a major antagonist named Kurmark was a mere human prior to his possession of the Blood Stone. However, the artifact gave him such a tremendous power to the point that Cadis Etrama Di Raizel had to unleash the Blood Phoenix attack to obliterate Kurmark.
In Noblesse, a traitor Noble, Lagus Tradio, was compelled to utilize the Blood Stone and was granted immeasurable power - so immeasurable that he temporarily overwhelmed Raizel, the most powerful of all Nobles. Only when Raizel utilized his own blood and essence into power was Lagus vanquished.
After Lagus' death, The Blood Stone embedded in his chest is broken into pieces and reduced to red ashes soon after, much to the dismay of Frankenstein(who had hoped that the pieces would hold a key to preserving his master's ever diminishing life)