There is a left luggage office in Tokyo Station connected to the area where they do JR Pass exchanges
https://www.jreast.co.jp/e/customer_...ter_tokyo.html

There are a lot of lockers in Tokyo station secondary corridors.
https://www.jreast.co.jp/e/stations/e1039.html

I have heard that the lockers in JR Akihabara station can get quite full but you shouldn't have a problem at 7/8 am. Stores in that area usually open around 10 am.

Sagawa also has a few left luggage and delivery offices in Tokyo
http://www.sagawa-exp.co.jp/ttk/english/

T-CAT also has coin lockers and a left luggage office
http://www.tcat-hakozaki.co.jp/en/floorguide/

ecbo cloak offers storage space in cafes and etc for slightly less than most left luggage offices
https://cloak.ecbo.io/en

Google for same day airport delivery in Tokyo brings up
https://airporter.delivery/
I've never used them.

Basically, if you're doing a day transit HND-NRT and arriving early, you can probably find a locker. They get more crowded as morning rush hour approaches and shops open.