The last time Han Sen saw Sonic-Thunder Punch, he fancied buying it. But back then, he was browsing for skills to be used by his other-self, Dollar. Therefore, he ended up buying Elephant-Disc Punch.
This time, Han Sen was free to buy Sonic-Thunder Punch as himself, from the Saint Hall. Having done so, he was keen to start into its practice.
Han Sen read Sonic-Thunder Punch's instructions and realized that it primarily dealt damage using thunder elemental power. In the instructions, however, it was noted that you could increase its potential by fusing the thunder with the sonic element.
Most people could only manage to possess and wield one elemental power. The most talented evolvers had been known to possess two different elements, but Han Sen had never seen the combination of thunder and sonic used before.