Pretty simple concept, it can be an item you can buy and you attach it to two fireworks. Upon lighting a firework with a connected fuse, it’ll then have a short delay based on the length of the fuse and light other connected fireworks.
Now, you might say “WELL IF FIREWORKS ARE CLOSE BY THEN CAN LIGHT EACHOTHER!!! POINTLESS ITEM!”
But, keyword there is “close by”. This is what the fuse is meant to eliminate, allows for fireworks to be lit regardless of if they’re close or not.
If the fuse were in the game, you could make more extravagant firework displays, since you can space them out at whatever distance you’d like (possibly making words/shapes with sparklers) or using the delay to your advantage to make complex displays.