Extreme
noun, な adjective
At the extreme edge, which is just the extreme.
きょくたん
This is a jukugo word, which usually means on'yomi readings from the kanji. If you know the readings of your kanji you'll know how to read this as well.
君は奇跡を起こすことができるかもしれない。でも、僕は君には極端なことは避けてもらいたいんだよ。
You may be able to perform miracles, but I want you to avoid doing extreme things.