Ari couldn't say what made him react that day. Some could assure that he was crazy, others that he was courageous, and a few probably would be right if they affirmed that it was destiny.
However, the only fact is that his body acted on its own. He rushed out of the middle of that crowd, his legs working out of will. His mind was still trying to register what his body was doing. It was a strange feeling.
When he realized, he was already near the carriage after passing through all the other guards and trying to get up on there.
His mask allowed him to do so because he didn't have any evil intentions when approaching the Princess. He wasn't even caring about getting near her. The only thing that the boy wanted was to stop that arrow.
During that course, Ari couldn't help but remember the words that Tani said to him that day. About punctuality.