It was a pain, but Billy had to make weapons made of diamond for anyone now. While that wasn't a problem since he was rich and couldn't sell the diamonds, it still was a pain. The materials were hard to work with, after all.
In any case, after he taught his friends the basics of Flash, he began to work with the diamonds. He also wondered what he should do to prevent them from being too flashy, but he gave up halfway. Those weapons were something that they should do only in rare moments, so they should just keep them hidden.
Regardless, as expected, Kate and Sarah learned Flash faster than the others since they were used to controlling mana every day with their training. They mastered it in just three days. The others took a while longer, but Billy didn't see any of them failing at doing so.
"Try not to use that too often, and also…" Billy said.