Eren was panting.
He had sent his mana circuits on overdrive to achieve this kill. Something he only learned recently.
One could amplify their spell's effect or boost their body's stats temporarily by sending their mana circuits on overdrive. It meant closing the mana points that were not useful and directing the compressed mana flow towards the mana points that were in use.
The spells would receive enhanced mana because of this, resulting in their effects getting amplified. If one did this while keeping a particular muscle group in their mind, then that muscle group would deliver more power and performance than usual as well.
The rankers who had sufficient control over their mana circuits could make use of this technique to provide an extra edge to their most potent attacks. Or to simply get out of a pinch.
