Compo items are items that can be attached to Weapons. Compo items permanently attach to weapons even when moved to the inventory, as such there is no way to remove a compo item from a weapon. However, it is possible to replace the compo item with another one. Doing so will destroy the previous compo item.
The player may place up to two compo items on weapons that are dropped from enemies. For two compo items to be attached to a weapon, they must not be identical. When a player hovers the mouse cursor on a weapon, regardless if placed in the Inventory or equipped, the weapon menu displays two black boxes at the bottom, representing the two compo item slots of a weapon. If the weapon has a Compo item attached, it will show in one of the black boxes.
List of compo items
Below is the list of all compo items in the Martian Series.