Monster Cells

Monster Cells are cells of Mysterious Beings, that can transform Humans into them.

Overview
If humans would inject those cells into themselves, they would supposedly start to exceed the limits of human beings and turn into monsters.However, this is not to be confused with breaking a natural limiter since this is just merely the mutation to turn human into a monster.

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