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, and if humans inject those cells into themselves, they 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 it creates. This shows that humans with strong natural power are able to transform into more hideous creatures than weak people who still maintain a lot of their human appearance. Benpatsu, for example only gained a third eye, sharp teeth, and sharp nails after eating a Monster Cell. Stronger humans such as Choze, Volten, Hamakuchi, or Gouketsu have more monstrous, inhuman appearances.

When a human becomes a monster, they experience bloodlust, sadism, ecstasy, insanity and a loss of both humanity as well as morality in which they will bend only on mayhem and destruction. Furthermore, the transformation effect is also very similar to when a human takes steroids, with some hosts showing intense pain upon ingesting. In exchange for this they gain great strength that allows them to surpass their old limits. However, this is not considered a limit breaker since becoming a monster is just putting a new limiter on the transformed human.

The monster cell must be eaten willingly or else the cell will have no effect. Apparently, eating more than one at a time, will kill the consumer.

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 offered him to eat a cell and become a monster.

Super Fight 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.

Bakuzan tries to eat multiple cells, but is apparently killed.