One of my favourite things in Japan is the opportunity to watch street performances or busking. They're mostly performed on weekends or on evenings in places where people stroll like train stations or in public parks. Performances are usually for free, but of course, offering money as gratitude is quite acceptable.
The first time when I saw a performance that drew in a good crowd was in Yokohama. Children as well as grownups watched the show and their reaction was quite positive. I later watched similar performances in Shinjuku and Ueno Park.
Sometimes monkeys are involved in the performances. The children seem to enjoy these ones a lot. Close to Ushiku Daibutsu, I saw a special show being held on a small stage but the performance I recall the most vividly was one team performing behind Senso-ji temple in Asakusa. I and my friend spotted a monkey dressed in a shirt and trousers who was patiently sitting and looking around before proceeding to eat a banana.
We joined the people already waiting and as soon as the performance started, more spectators arrived. There were just two participants, a young man and a monkey who performed many tricks, seemingly without prompting. They looked good together, as if they were friends. Their final bow at the end of the show produced lots of laughter. Of course, we didn't skimp on our rewards!
I quite often saw people singing on the streets, but a most memorable scene was near Mito Station where people gathered around the singer, singing with her. I thought that was nice as everyone seemed happy.
While not busking, festivals in Japan are like street shows. I watched a cultural Awa Odori dance accompanied by traditional Japanese music at the Kagurazaka Matsuri in Tokyo. I also saw dancers wearing beautiful Okinawan costumes at a festival in Ikebukuro. You'll also find Internationals festivals like the many performances at the Festival of Asian Countries in Harajuku.
On weekends there is always good opportunity to watch a street performance or festival. Joining the audience is a great way of getting to know the people.