He had been able to keep it up by making the barrier extremely thin. Enough to handle a normal, mundane human, yet nowhere strong enough to hold a magical being.
However, he wasn't thinking about the barrier itself but the side-effect of removing the light, making them all go blind.
Since he'd gotten his dark magic, he had been developing it toward fitting his aggressive, close-combat style. Then, if things got rough, he would switch to Synchro, enhancing his physical prowess but losing his access to his magic.
'Aren't I just making my dark magic a poor substitute for my Synchro?'
There was nothing wrong with changing his dark magic to suit him. Most would say that doing so would be the best for his growth.
Yet, was there a point in doing so when there was a far better option in his arsenal?
'If I don't want my dark magic to hit a wall, I need to change how I utilize it on a fundamental level.'
As for how he would shift it, he already had an idea in mind.