I would caution against leaving it in the lounge. As I recall it was just a communal area with places to put your luggage. And during the day the Sakura Lounge can get pretty f'ing packed. It's not worth the risk.

There are coin lockers on the 3rd floor departures area. Conversely if the carry on is not that big you can take it with you to to Tokyo and leave it at the coin lockers there. I always use the Shinagawa Station and there is always a ton of lockers available. Even the biggest one is only 400en for a whole day.