if you intend on watching this anime you only really need to watch the first two arks as after that point this show becomes very repetitive.
each and every ark consists of them being attacked or trying to defeat a foe seamingling much more powerful than themselves.
they always strugle for very lengthed out episodes then at the last minute they get some sudden burst of strength and over-come their foes.
this gets very boring and it goes for EVERY single episode and trust me when you have watched as many episodes as i have you will regret wasting your time with this show.
i did enjoy this show for quite some time but after watching so many episodes the series started to feel very dry but i felt pressured to continue watching this show.