The [Water Bullets] that Chopra had blocked earlier radiated a chilliness. The bullets didn't ice over, but their temperature seemed to have plummeted in ways that the Runes weren't ready to react to. Or rather, they physically slowed the capability of the Runes to react.
Theron had already noticed earlier that when Chopra's armor took action, it needed elasticity and flexibility. First, it would absorb the attack that came, then swiftly change to store it, and then prepare it for action afterward.
If any one of these three processes was stalled, it could lead to a backlog that would allow the Runes to be easily overwhelmed. And other than a direct attack with Soul Mana, there was little that could do this better than cold Mana.
Mana wasn't just an external energy—it was part of the fabric of reality. And much like the laws of physics dictated, cold energy moved more slowly. In fact, this was one of the greatest weaknesses of Ice Mancers.