You must have heard this phrase in Japanese manga or anime couple of times. This is a combination of two words.
疾風(shi-puu)
疾(shitsu)= In this context, this Kanji modifies the latter 風 to express ‘very fast’.
風(huu)= It simply means wind.
Then 疾風 means ‘very strong wind’ literally. When interpreted, it implies taking prompt actions when dealing with fast changing situations.
On the other hand,
迅雷(zin-rai)
迅(zin)= Actually, it means speed like thunder.
雷(rai)= It simply means thunder.
However, 迅雷 means not only ‘speed’ but also ‘violence’.
Finally,
疾風迅雷= This Kanji combination expresses ‘fast and strong’ like thunders. It implies being prompt and resilient when dealing with fast changing situations. We live in a world where change is constant and inevitable. But just like changing clothes, it’s necessary. So, we need to improve our reflexes when dealing with them. We need to be ready and quick to act as occasion demands.
If you are interested in these Kanji, you may simply copy them from this website and use them as you please. Make them yours!