As others have said, it could be a bit of a squeeze, but you’ll definitely be able to do it. A lot of people get on and off the Marunouchi Line at Ginza (see below). If you were talking about Ginza Line between AkasakaMitsuke and Shinbashi (especially on a rainy morning), I would think twice about it, but the Marunouchi Line isn’t so bad. One thing to think about, however, is where to get off (if you take the Shuttle or Access Narita). The bus will stop at Tokyo Station first, but it’s a loooooong walk from the bus stop to the Marunouchi Line (basically you have to go from the Yaesu side to Marunouchi side of Tokyo Station), so it might be wiser to stay another 5 minutes on the bus to go to Ginza (even though you’re going in the ‘wrong’ direction). Then you just have to take the lift down into the station and the Marunouchi Line is very close by. That’s what I would do!