The Ego Block is an integral part in the struggle between the Ark Faction and the Interception Faction. This largely because currently, no technology in Earth is capable of destroying the Ego Blocks, causing Ark Faction supporters such as Salty Dog to believe that continuous struggle against the Planetary Gears is a loss of time and would cause humanity's doom, putting their faith instead on the Kivotos Plan.
This is evidenced by the seemingly destruction of Malkin's and Zinbalt's Ego Blocks at the hands of the Earth Engine and Nebula Engine as even though they succeeded in blasting them at point-blank range, the Ego Blocks quickly regenerated.
Currently, the Ego Blocks reside in the Cocoon, which is the core of the Planetary Gear ship the Oberon. The planned Operation Summer is set to destroy the ship's core and with it the Ego Blocks, thus putting a definitive end to the Planetary Gear threat.
Although Ego Blocks can be destroyed by the Plasmagnum and its upgraded forms, Siren can regenerate their Ego Blocks and bring back any destroyed Kiltgang body that fell with it. According to Amara the only condition to be able to regenerate the Ego Block is that the respective avatar body is alive, therefore Siren would also be able to make any regular human into a Planetary Gear if she so desired, including Neotenies, although in their case they would have to cast aside their Livlasters as they are incompatibly with beings that possess an Ego Block.
As explained by Puck the reason for this incompatibility relies on its namesake, the Ego. Any being regardless of whether they are alive or not, can manifest an Ego Block so as long as they have a large amount of desires, which is the reason why Puck can also manifest its own Ego Block, but as described by Setsuna, this makes them "masses of swollen ego" which is the reason she believes the Livlasters reject them. This is rather evidenced by Puck's possession of Hana Mutou. Despite the fact he controlled her body, the Blossom Livlaster did not function at all, as it sensed the differences between the two.
It is also revealed that beings with Ego Blocks are the only ones capable of using a Planetary Sign and that only an individual with an Ego Block can break them.