Students at the Scarlet Heaven Academy had to complete a set number of missions each year.
Of course, one could also complete a large number of missions in a single year, then complete no mission at all for the following several years. This was because cultivators would cultivate in seclusion for months on end after reaching the Immortal level. In fact, some would even cultivate for a few years.
The Academy couldn't expel students for such a reason, right?
The mission that Shui Yanyu accepted wasn't too difficult. Although it required them to exterminate pirates, it didn't require them to exterminate the entire pirate fleet. They only needed to kill a certain number of pirates. Moreover, this mission could be completed over and over again. As a result, the power of the pirates would be gradually weakened until they were eventually completely destroyed.