Both the Sendai City Bus Company and Miyagi Kotsu Bus Company (red) offer prepaid cards.
Both companies' cards may be used on either Sendai City or Miyagi Kotsu buses.
Each card comes with a premium as follows:
1000yen -> 1100yen,
3000yen -> 3360yen,
5000yen -> 5850yen.
Sendai City bus card
Miyagi Kotsu bus card