Summer in Tokyo is always related to fireworks, particularly on weekends; Asakusa and Odaiba are maybe the most popular ones. Crowds at these locations mean extensive planning to get the right place to sit, or you end up having to wade through the crowds and try getting a glimpse of the fireworks. The equivalent event in the harbor city of Kobe is the Minato Kobe Marine Fireworks Festival.
The event is held on the first Saturday in August every year, a spectacle of over 10,000 fireworks which can be watched and enjoyed from various locations around the Kobe Port area. A good spot for example is Meriken Park near the popular landmark of MOSAIC Kobe, although I personally prefer to travel two stops from Sannomiya on the Port Island line to the Port Island station. The spot just outside the station attracts a few people but this is not comparable to the crowds in Tokyo. You can get a clear view of the firework shots being fired from the waterfront with the beautiful city line of the Kobe Port area in the background. Port Island has very few shops or convenience stores around, so pick your snacks, beer cans, soft drinks etc. to enjoy during the event from Sannomiya itself.
Thin crowds at Port Island (Meriken Park gets quite crowded though), a great view of the fireworks complemented with the waterfront of Kobe Port and Mount Maya in the far background makes the festival one of my best experiences of summer fireworks in Japan.
If you plan to attend the event you may want to check the weather before you make the trip. Rains may lead to cancelation of the event which the organizers decide by 3pm on the day of the event.
There is a less known spot, but quite a romantic one, to view the fireworks and mostly couples can be seen at the Venus Bridge watching the fireworks from a distance. In Tokyo, I have seen fireworks from a height only, that means from high-rise office buildings; the natural setup of the Venus Bridge on Mount Maya in Kobe is a different experience altogether—highly recommended.