Interestingly, even though all the elements in nature had their particular characteristics when it came to shaping them through mana, An Elementalist needed a strong image and a solid concept to strengthen his control over mana and give the element a predominant characteristic of it.
In the same way, Desmond applied the concept of the softness, malleability, and weight of water. Other elemental adeps could associate various images to the elements under their control, giving their attacks greater power or greater precision.
The same applied to Cecilia, who was currently using density on light mana under her control; she thus saturates the room with light mana so thick it makes it hard to even breathe.
Hence came the strong sense of oppression that had filled the room. However, this could also be attributed to the enormous mana fluctuations emanating from Cecilia at that instant, something any mana user would be susceptible to.
