There are no hotels at Kitahiroshima Station, so your base of operations will be Sapporo.
From JR Sapporo Station, take the airport-bound train (Rapid Airport), which takes about 20 minutes (￥540 from Sapporo to Kitahiroshima).
If you are coming directly from the airport, take the train (Rapid Airport) bound for Sapporo, which also takes about 20 minutes. (From New Chitose Airport to Kitahiroshima is ￥560).
There is a shuttle bus from Kitahiroshima Station. It takes about 5 minutes to get to the stadium. (¥200 cash or VISA touch only).
It is also possible to walk from the station to the stadium. It takes about 20 minutes.
https://stadium-experiences.com