There are actually 48 episodes, 2 movies (about ep 1 - 28) and a combine ep for this anime (29 - 48).
The first 13 ep are just introducing how things work and stuff, and it get even better afterwards.
I am Chinese, so I watch it in the original site bilibili and be able to understand it fully (including some of those chinese jokes).
This is an amazing anime, and I totally recommend it, I cried multiple times so prepare tissues if you cry as easy as I do.
The anime gets better from ep 14 but ep 1- 13 are important as well
because they tell you what is actually happening.
The story is actually a lot deeper than what it shows you from the first few episodes :)
and all the characters are amazingggggg!!