by ep 9 (or is 10?) it does introduce a larger story... and what do people have against episodic shows??? hell Cowboy Bebop was one of the best shows i've seen and there wasn't any emphasis on a larger plot...
This show I think is good and even if the first half is mostly episodic its irrelevent... and in the end... there IS a main story that has been hinted at since the 1st ep...

it is not filler... simply rapidly wrapped aventures that tie in into a bigger universe... fillers do not really tie in and simply pass time with NO development whatsoever.