K4-Level was special, not only because by this point a Phantom had already created all the Keys and unlocked the Lock, but because it was the end of the road, literally.
At lower levels, a Phantom always had the opportunity to grow stronger, evolve, and move forward, drawing closer to the summit that was constantly receding further and further.
K4-Level was the longest of them all. It took all the Phantoms far longer to collect all the Grand Stars at the Path Construct than it did to complete the entire path leading up to it.
The best and worst thing about the K4 Level was that it could be the last one, both in the First Circle and in general. It all depended on the Phantoms themselves.
Most K4 Phantoms stopped at this level and never went any further. They simply couldn't break through the barrier.
As a result, they no longer had any new evolutions or power-ups, since they had already reached their peak as both humans and Phantoms.
