Monster Cells

Monster Cells (怪人細胞, Kaijin Saibō) are cell-like objects that can transform humans into monsters upon ingestion.

Overview
Monster cells have the appearance of a pulsating cell made of flesh, and are about the size of a normal human hand. If a human ingests a cell, they undergo a physical and mental transformation that allows them to exceed their human limitations and turn into monsters.

Monster cells build upon the talents of the subject, but it comes at the cost of losing the potential to grow stronger. The monster cells also depend on the potential of the human itself to create monsters. The stronger the human, the stronger the monster transformation will be. 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, and Rosie only gained an abnormal muscular physique with protrusions sticking out his back. On the other hand, stronger humans such as Choze, Volten, Hamukichi, or Gouketsu have more monstrous and inhuman appearances.

When a human becomes a monster, they experience bloodlust, 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 ingestion. In exchange for this, they gain great strength that allows them to surpass their previous abilities. However, this is not considered a limit remover since becoming a monster is just putting a new limiter on the transformed human. A particular weakness when a human becomes a monster through this method is that they will become extremely reckless due to the heightened bloodlust caused by the cell before learning to hone and control their new instincts. For example, newly transformed monsters often attempt to attack without gauging the power of their opponents. Benpatsu displayed this reckless behavior when he charged directly at Suiryu, only to be knocked out by one kick. Bakuzan also showed this behavior, believing that he is stronger than all S-class heroes and monsters. This led him to attack Gouketsu, but the latter easily stopped his attack. The Monster Cell also brings out the worst of a human's personality when they become a monster. In the case of Bakuzan, not only did the cell makes him more brutal and sadistic, but also showed true character he was hiding in 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 and intelligence, like Hamukichi and The Three Crows, and become little more than monstrous animals. Some stronger willed individuals are able to alternate between their human and monster forms. Such was the case with Haragiri, Gale Wind and Hellfire Flame, 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 human body cannot handle the power of multiple cells all at once. In this situation, the monsterfication will be halted for some time until it can be completed. It was later revealed by Gyoro Gyoro that eating multiple monster cells is the same as consuming one since monster cells simply transform abilities possessed by the original individual.

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, this resulted in him not undergoing a transformation and instead having an upset stomach afterwards, showing that cooking a Monster Cell renders it useless.

The "Monster King" Orochi is said to produce these cells.

History
At some point in the past, Gyoro Gyoro and Orochi captured and tortured 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 ate the cells to become monsters.

Super Fight Arc
Haragiri explains using Monster Cells to turn into a Mysterious Being before the meeting of the Council of Swordmasters, and after consuming one himself and attempting to kill Atomic Samurai he is quickly defeated.

When Gouketsu and the monsters crash the Super Fight tournament, they demand that the remaining fighters eat Monster Cells and transform or die. Rosie eats one of the cells and becomes a monster, but is quickly killed by Choze, who becomes a monster as well. Volten, Benpatsu and Hamukichi also eat cells and become monsters, though they are all defeated by Suiryu before long. Bakuzan tries to eat multiple cells at once in order to gain a stronger transformation, but apparently dies in doing so. It is later revealed that he did indeed transform and attacks Suiryu in his new form, almost defeating him before being killed by Saitama.

Meanwhile, Nyan uses Monster Cells to transform many of the prisoners in Smelly Lid Prison and takes them with him back to the Monster Association's hideout.

Speed-o'-Sound Sonic is given a Monster Cell by Hellfire Flame and Gale Wind in a bid to get him to join the Monster Association. He eats the cell after cooking it in wine, but it has no effect aside from give him a stomach ache, as cooking a Monster Cell renders its morphing abilities ineffective.