Alex sent out a steady stream of Metal Qi while doing his best to keep the Intent as strong as he could. The first few minutes were fine, but after that, he started noticing strain in his body that came from applying too much Intent.
He got a wild mental pain similar to when he had to deal with Intent from outside.
'What's going on?' he wondered. He had never had to send out Intent for this long, and it seemed to be causing some problems. At the same time, he noticed for the first time that his intent was causing his Spiritual Energy to decrease by a decent amount.
It wouldn't be very noticeable if the Intent usage was short, but this long he noticed the lack in his Spiritual energy. Either the spiritual energy was dealing with the ramifications of him sending our Intent, or it was fueling the Intent itself.
Either way, his spiritual energy was depleting and his Intent was the cause for it.