The annual Koto-ku Fireworks Festival will see 4,000 fireworks going off—making it about a third of the size of Tokyo’s biggest fireworks festivals. It’s still a good, colourful show though, in a nice spot—Sunamachi Mizube Park, near the Arakawa River. Expect a crowd of around 300,000 spectators. The venue is 15 minutes from Minami-Sunamachi Station. Launch-time is 7:30pm and although the event is rain or shine, a typhoon will postpone it by either one or two days.
Note that due to the olympics, the festival has moved from its regular August schedule to June for 2020 – it is expected to return to normal in 2021.