Welcome to FT, and check out the Japan sticky at the top of the forum which tells you all sorts of good stuff about Japan, including about the JR pass.

To give a proper answer to your question, it is important to know not only that you are arriving at Narita, but what airport you are departing from.

Under the assumption that you are also departing from Narita, let me make a few short comments.

1. The only rail pass that will allow you to include Tokyo and Kyoto (let alone Sendai) is the all-Japan one.

2, If you would just use the pass for Tokyo-Kyoto-Sendai-Tokyo, you will come out ahead with the pass over buying individual tickets. Any use to/from Narita and local use in Tokyo or elsewhere will be a bonus.

3. If you are there for a full week (i.e., Sunday to Sunday), you will likely have to pay for one trip to or from Narita, as the pass is only good for 7 CALENDAR days. I.e., if you validate it to start on a Sunday, the last time it is good is the following Saturday at midnight.

Again, welcome to FT!