Monster Cells

Monster Cells (怪人細胞, Kaijin Saibō) are cells that can transform Humans into Mysterious Beings.

Overview
They have the appearance of pulsating sludge, that if humans would inject those cells into themselves, they would supposedly start to exceed the limits of human beings and turn into monsters.

The Monster Cells also depend on the base natural power of the human itself to create monsters. The stronger the human, the stronger the monster is it creates, which shows that human with strong natural power is able to transform into more hideous creature than weak people who still maintain a lot of their human appearance (in the case of Benpatsu since he only has third eye, sharp teeth and sharp nail or Rosie only has massive muscle growth when transforming into monster while strong human like Volten, Hamakuchi, Choze or Gouketsu transform into creatures that completely inhuman in appearance)

When a human becomes a monster, they will experience bloodlust, sadism, ecstasy, insanity and lost of humanity as well as morality in which they will bend only on mayhem and destruction. Furthermore, the transformation effect also very similar when a human takes steroid showing that some human experience intense pain upon ingesting. In exchange, they will exceed the limit of a human in power. However, this is not considered to break a limiter since becoming a monster is just putting a new limiter on the transformed human.

The monster cell must be eaten raw and willingly or else the cell will have no effect.

The "Monster King" Orochi seems to be the source of the cells.

History
At some point in the past, Gyoro Gyoro and Orochi captured Gouketsu and forced him to eat a cell and become a monster.

Monster Association Arc
Haragiri used Monster Cells to turn into a Mysterious Being during the meeting of the Council of Swordmasters.

Rosie eats one of the cells and becomes a monster, he is then killed by Choze, who becomes a monster as well. Volten, Benpatsu and Hamukichi become monsters as well.