Rental phone 3 months

Hello! i have been searching through the web on options for data cards + rental phone in Japan, but i haven't found satisfying answers. Here is my issue:

I will be in Japan for 3 months, in a rural area belonging to Kashiwazaki-shi (not in the city itself) and since i found out that probably i can't use my phone on most rural areas, i was aiming for a data-only (i only need to send overseas e-mail on the phone) plus rental phone service.

Any ideas on prices? Or where to get this kind of info? Is this too expensive? Because i found several plans with prices/day or /week but offering only the card and without phone rental service.

Thank you in advance!!

i found out that probably i can't use my phone on most rural areas

That's very probably not correct. What kind of phone do you have?

Thank you for your reply!
Well, I hope you are right. Mine is a Huawei Y300-0100. It iscompatible with 3G 2100Mhz, buti read somewhere that this frequency only exists in big cities and that In the countryside only 800Mhz exists.

Yes, that's how Docomo's 3G network (FOMA) operates. You can check the coverage map here: http://servicearea.nttdocomo.co.jp/inet/GoRegcorpServlet?rgcd=02&cmcd=LTE2&scale=250000&lat=38.265868&lot=140.875533

Areas in pink are regular FOMA (2100 MHz), areas in yellow are "FOMA Plus Area" (800 MHz).