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 blood lust, sadism, ecstasy, insanity and a loss of both humanity as well as morality and even rational thinking 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. A particular weakness when a human becomes a monster is that they will become extremely reckless due to the heightened blood-lust caused by the cell before learning to hone and control their new monster intincts. Examples of this recklessness is that a newly transformed human will often attack an opponent many times stronger than themselves like Benpatsu charging directly at Suiryu only to be killed by one kick to the neck or Bakuzan believing that he is stronger than all S-Class Heroes and monsters to which he attacks Gouketsu without hesitation only to be stopped by the latter's superior strength. The Monster Cell also brings out the worst of a human's personality when a they become a monster like in the case of Bakuzan not only does the cell makes him more brutal and sadistic but also showing what he truly is from the deep of his black heart: a bully who wanted to become strong just to prey on the weak.

If the consumer has a weak will, they will lose their ego, like Hamukichi and The Three Crows. In the case of stronger willed individuals, not only do they gain a monstrous power boost, but can also will their transformations on and off in order to pass off as human. Such was the case with Haragiri, Hayate of the Wind and Flame of the Hellfire, all of whom were experienced warriors with a mastery of mind & body.

The monster cell must be eaten raw and willingly or else the cell will have no effect. Apparently, eating more than one at a time, will knock out the consumer since the body of the human cannot handle the power of multiple cells at once. In this situation, the monsterfication will be halted for some time until it can be completed. It is unclear if the consumption of too many of these cells will result in death, and it's also unclear if eating multiple monster cells with multiply the consumer's power or if it will remain the same as if the consumer ate one. Speed o' Sound Sonic cooked a Monster Cell in wine after deciding to eat it and become a monster, reasoning that no one would eat something dirty and raw without knowing where it was from. However, he did not immediately undergo a transformation and instead had an upset stomach afterwards. This may indicate that cooking a Monster Cell renders it inactive.

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.

Gouketsu then gives the cells to his disciples, who become The Three Crows.

Gale Wind and Hellfire Flame eat the cells to become monsters.

Super Fight Arc
Haragiri used Monster Cells to turn into a Mysterious Being before 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. It is revealed that he indeed transformed and attacks Suiryu.

Nyan transforms many prisoners in Smelly Lid Prison.

Speed-o'-Sound Sonic eats a cell after cooking it in wine.