Gensokyo/Kusanagi

The Kusanagi is a Pre-Hardmode sword. It is the weakest sword in the mod. However, its alternate fire allows its wielder to change the weather. In a desert, this starts (or stops) the Sandstorm, whereas everywhere else it starts the Rain event. The cooldown of the alt-fire is 120 seconds, which makes it the longest cooldown of all alternate fire modes.

It is sold by the Curio Trader. Of all the items sold by him, the Kusanagi is currently the only one that does not have to be unlocked by defeating a Boss.