It will be a little bit of both, there will be monster raising but that will only be (easily) done with baby monsters, monsters that pose a threat to civilians will have to be hunted. When you say they killed an innocent creature, I'm assuming you mean the Lagiacrus, if you don't in not sure what you do mean. For the Lagiacrus being killed, Nergi was quick to act, so both Ruby and Yang decided helping her would be a good idea. The Lagiacrus was also to close to the town to be safe, it was already aggressive and angry, and despite it not having the normal colors of a Grimm, anyone could assume it could be a new species of Grimm (though I, personally, highly doubt that). Sorry if this comes off as a bit of a rant, I just wanted to answer your questions the way I believe to make sense in the context of the situation.
