No we are not Homeless;) Futako Tamagawa station is on a bridge which goes over the Kanda River (snakes throughout Tokyo) and many people go there on the weekend for BBQs, Sports etc. There is grass for ovals but people gather under the bridge for shade and cover, and bring their own portable BBQ gear! As well as music, tarp sheets, tents and of course alcohol. Theres even 3 old Japanese guys who manage all the trash.
We setup and had snacks and drinks in the afternoon sun. It was also a small Sayonara party for Mayuko who leaves for Canada on Thursday!!