Vocabulary consisting only from characters you are able to read
The sum of inner angles of a triangle is π.math
必要(な)
ひつよう(な)
(1)necessary/needed/essential/indispensable/(n) (2)necessity/need/requirement/(P) adj, leda1
外伝
がいでん
(1)supplementary biography, (2)anecdote, side story, spin-off mix