I see these super narrow buildings around Tokyo as well. Asked a friend years back about why, was told that things get built to property lines and when odd splits due to inheritance or only part of a lot of land being sold you end up with these weird shaped or small lots. Cant let the land be useless so people build on it up to what it will accommodate.
@buddybradley you are right thats indeed a meeting place for esperanto speakers or possibly the HQ of an esperanto association.
