I would take the bus to HND, find a locker and dump your stuff, take the monorail to the Hamamatsucho terminus (15mins), then you've got a world of opportunities - Harajuku ( as suggested), Asakusa, Odaiba (very close to Hamamatsucho). The Tokyo Monorail website (tokyo-monorail.co.jp) has tour suggestions.
You could take the N-EX train from NRT to Tokyo. There should be lockers at the station, but I've heard rumors that the lockers may be too small for a roller. They have a left luggage office, but it closes at 20:30.