During end of July and the entire August, there are a lot of Fireworks festivals (Hanabi). These are not any small fireworks, but large one, usually lasting about 1 hour.
For the most popular ones, you need to be very early if you like to get a good seat. Very early means about 7-8 in the morning… Don’t expect that you can get a good seat just an hour prior the fireworks start. All places are very well marked and clear rules how you should sit. So it is not standing in a cramped space with a lot of people, but rather sitting on the grass or even on the paved roads where the officials tell you to sit.
If you have the chance, it is for sure an experience worth visiting.
How to get there
There are several sites with the schedule and location of the events. Search for e.g., Hanabi Tokyo to get the schedule for the area.