If you are about to explore Sapporo during weekend, I highly recommend you to get the Donichika Ticket for subway rides.
Donichika Ticket is a one-day (subway only) unlimited pass that you can use on Saturdays, Sundays, national holidays and year-end/New Year holidays (Dec. 29 – Jan. 3). It’s 520 yen for adults and 260 yen for kids (7 to 12 years old).
You can get your ticket at vending machines in any subway stations.
and yes,Cash only.
Other unlimited passes
One-Day Subway Pass
This is a money-saving pass that allows unlimited rides on subway trains for the whole day.
Adults: 830 yen; children: 420 yen
This is a one-day pass that can be used for streetcars on Saturdays, Sundays, national holidays and year-end/New Year holidays (Dec. 29 – Jan. 3).
One Dosanko Pass allows an adult and a child unlimited rides on streetcars for the whole day.
For more information, visit City of Sapporo website, Fare and tickets page