She's standing on the roof of an actual ferryboat moored in the Kita-Shinagawa marina just off the Meguro River that leads to Tokyo Bay.

https://www.google.com/maps/@35.6219713,139.7413712,3a,75y,355.98h,85.98t/data=!3m6!1e1!3m4!1sOwXh2ljv-oL2wyek9sT1qA!2e0!7i16384!8i8192