This article introduced some hidden places in Tokyo, which I think can help you.
July to early August is when Tsuyu, rainy season ends in Tokyo and real summer starts!A local Japanese common things to do in July/early august: (many people take summer vacation)
1. Go to fireworks festivals.
There are many fireworks festivals held in Tokyo from July to August. People put on Yukata, a Japanese summer kimono-like traditional wear, and visit those festivals to watch fireworks. Some of the famous one in Tokyo are Sumida River Fireworks Festival (http://sumidagawa-hanabi.com/) in Asakusa, Jingu Gaien Fireworks Festival (http://www.jinguhanabi.com/) in Omotesando, and Edogawa Fireworks Festival in Edogawa-ward.
2. Enjoy street foods at festivals
Festivals in summer are special to Japanese. We dress up with yukata and visit festivals to watch Omikoshi (Shinto floats for festivals) parades and play and eat at "Ennichi", the strolls street. There are many common food and games at Ennichi. For food, Okonomiyaki, Takoyaki, Banana Chocolate, cotton candies, Apple candies to name the few. For games, Kingyosukui (fishing goldfish), Shateki (shooting), Yo-Yo Sukui (fishing water balloon), etc.
3. Go to "Beer Garden"
"Beer Garden" is a special place pops up in summer. It commonly appears on the rooftop of department store, and is the place to drink beer and enjoy food outside. People visit Beer Garden after work to drink with colleagues and friends!