Her face was pale. The ‘bending’ just now made her use a lot of her mental energy.
Even though the scale was different, regardless if it was bending or future sight, the whole brain still needed to perform calculation. As for the mental energy, it was better to refer to it as a burden, because it caused wear to the brain and took up calories. Future sight only needed to replenish its user’s glucose level to be used again, however if it was at the power level of Asagami-san’s bending powers, the burden will be directly reflected on the user…. Worst case scenario, after she used her bending abilities, she will not exist anymore.