Can you guess my book?

1.This book is about elements there are 7 main Characters.

2. one has nunchucks, another has shurkeins  , another has a sword, and the other one has scythe

3.and the youngest has no weapon

4.there are 13 seasons

5.the oldest is the one with shurkeins 

6.and the teacher is an old person

7.and the second to youngest has no weapon 

they have different elements

what was my book?