unusual event; strange occurrence; strange phenomenon; something abnormal; change (for the worse); accident; disaster
体に異変を感じたらすぐに医師に相談すべきだ。
If you feel something unusual in your body, you should consult a doctor immediately.
空に異変が生じ嵐の前兆かと騒ぎになった。
Something unusual occurred in the sky, causing a commotion about a possible storm.
生態系に異変が起きていることが判明した。
It was discovered that an unusual change is occurring in the ecosystem.