Marunouchi and Nihonbashi in the same day?

Greetings

I was wondering if these two areas could be visited (at a leisurely pace) in the same day. They seem to be relatively close from each other but one of the things I learned in my first trip was that Google Maps makes everything look way easier and accesible than it really is, specially if you go by foot.

I wouldn't have problems with investing a whole day to each place, but I don't know if they are interesting enough to keep my interest for that long. The Marunouchi plan can be filled with the neighboring Ginza or even Shimbashi, but when it comes to Nihonbashi (perhaps Shin Nihonbashi, as the flashy area seems to be on the other side of the river) I can't come up with good combinations.

Any suggestion will be most appreciated.

It fully depends on your pace and on how much you want to see. Generally speaking, I think the two districts would make a very good 1-day program for the average traveler. But slow travelers with a deep interest could also spend entire days in each district. Likewise, some people would not be able to find enough attractions in these two places to keep them busy an entire day, especially fast travelers, travelers who are only interested in top attractions and those not particularly interested in shopping.

Yes, Marunouchi and Nihonbashi areas can be explored by foot at leisurely pace. Whether to spend one or two days depends on your interest. Marunouchi is considered the financial district (mostly banks and office buildings), but there are few interesting shops and restaurants in addition to the Tokyo Station itself. Nihonbashi area has more historical points of interests and I can see myself spending a good part of a day there.

Really depends what you are interested in. There are some cool (hidden) gems in the area (I had a fascinating visit to a paper shop a coupe of years back), but for other people they are just city blocks of stores/offices/restaurants etc. For some other guests we had in May 2017 they spent half a day browsing the book and print stores in Jimbocho (also not far away).
As for "is it far", about 1.6km from Hibya to Nihonbashi stations in a straight line - so not hard to do by foot.

Regarding Marunouchi, just visiting the station and the surroundings of the Imperial Palace is interesting enough for me, and since it seems to be near other interesting places like Yurakucho and Ginza I hoped that I could have a relaxing day strolling through the center of Tokyo and feeling the urban atmosphere.

I think I'll just pop up at Tokyo Station not too early in the morning and start exploring around instead of following a route. If I end visiting Shimbashi I guess it will be on a different day.

Thanks for your help!