Dynamite

Dynamite is the first explosive item that is found in the game. While slicing your fish for gold, dynamites will randomly fly up into the groups of fish. If sliced, they will explode, and you will lose all of your gold and fish aquired during that fishing run.

If you purchased the Kusanagi no Dynamito Katana for $2.99, you are given the ability to slice through dynamites, and you will not lose your game, as the dynamite will not explode.