Originally Posted by Finalcall

Yes, definitely. Narita has many of these automated luggage storage lockers. Your United and ANA flights are in Terminal 1. After exiting customs, go to the elevator area and you'll find many lockers. There are three different sizes ranging from around 500 to 1000 yen. They take Suica (the Tokyo metro card) and I think cash also. Rates are from midnight to midnight. You will use the receipt to unlock your locker when you return.