yea I don't want to spoil it and really what's mature and not mature can kinda be left in the eyes of the beholder, here's an episode description list, you can read through and decide for yourself.
link (scroll down to S2) Alois has a disturbing past on his childhood and there is blood/fighting in the season but with the exception of a few things I don't think it's that bad, really though it's in the eyes of the beholder. The sexual stuff is more implied than shown, but it can be rather disturbing as it deals with under aged kids...... although I don't think you should skip it as it does play an important role in the character development of the series, so you may need to decide if you really want to watch this season or not, it is completely different from the manga and most people will say that it's not that good of a season anyway, and I honestly don't recommend skipping the stuff because I personally think it plays a large role, so if it sounds to you like something you don't want to see then maybe save this for another time.
