Tokyo, as a global metropolis, is something to be experienced. There's genuinely little to see, an afternoon on a tour bus will cover most of the sights (caveat; the architecture is avant guard and spectacular, just visit the Prada building on Omote Sando) but that isn't the point of the city. Tokyo isn't there to be seen, it's there to be experienced. So enjoy it, every single day.
When I first arrived in Japan I was taken to a Live! as it's known in Japan, or Live House if you actually want to know what it means, that went by the name of Bauhaus. This was in the old days before it relocated to the environs of the Hard Rock Cafe in Roppongi. No larger than the three tables if boasted, the band in the corner fronted by Ziggy Stardust on lead vocals (turned out his day job was a professor at Waseda University) and a bass guitarist you'd freak about if your daughter brought him home after a date.
They would occasionally invite guests to play with them too and Doctor Suzuki, in his suit and tie, walking on stage transforming into Jimi Hendrix and the girl who spoke no English (at all!) could belt out the Janis Joplin classics like I've never heard before. I once witnessed as a guy in the audience ask if he could try out the drums. And. He. Nailed. Black. Dog. So don't worry about visiting the gates of the Emperor's Palace or taking the boat on the river to see concrete, rather, experience Tokyo, it's the greatest show on earth.