N4

とされている

To be considered, To be deemed, Be regarded as, Be accepted as, To be said, To be accredited with

世界せかい
にん
魔女まじょ
いる
いる
It is said that there are five witches in the world.
まだまだ
冒険ぼーけん
しゃ
必要ひつよー
いる
Adventurers are still very much needed.
それ
きっかけ
変わっかわっ
いる
It is said that (something/someone) changed because of that trigger/opportunity.
失わうしなわ
いる
もの
どんな
もの
です
What kind of things are said to have been lost?
それ
ゆえ
非常ひじょー
危険きけん
行為こーい
いる
Therefore, it is considered to be a very dangerous act.
必要ひつよー
いる
から
Since (I/you/we/they) are needed...!