The Edogawa Fireworks Matsuri is one of the best Fireworks festivals around Tokyo. Beautiful location, many food stalls and of course amazing fireworks! Be sure to come early to get a comfy spot (might be useful to bring a leisure sheet, as you have to sit on the grass) to enjoy the fireworks. They can be seen from both sides of the Edogawa River. The fireworks are absolutely stunning and the atmosphere is great! It might be crowded, but Japanese people respect each others private space, so once you’ve got yourself a place to sit, there’s no need to worry.
You’ll have to walk a bit, but if you just follow the crowd then there’s no chance of getting lost. It’s about 20 minutes walk from Shinozaki Station (Toei Shinjuku Line) and 30 minutes from Koiwa Station (JR).
This festival usually takes place in the first weekend of August.
Be sure to check the official date and time on their website (in Japanese): http://www.city.edogawa.tokyo.jp/hanabi/