You can book a train package of Limited Express train, Hokuto, and Shinkansen Hayabusa from Sapporo to Tokyo online here.
You can have an available seat at non-reserved seat cars only.
Reserved seat will be assigned from Shin-Hakodate-Hokuto to Tokyo
You can choose the following options for receiving tickets:
For detail, please check [From Purchase to Delivery] page.
Regular seats used on Reserved cars and Unreserved cars of Shinkansen. Consider it as "economy class" seat.
Better seats with more space than ordinary seats. All Green Seats are reserved only. Consider it as "business class" seats.
Your seat is reserved and secured when you book your tickets. Head to the station with a peace of mind.
Seats are the same as Ordinary Seat.
Better seats and free blankets. Popular among Japanese business persons, executives and people who
Know as "First Class" of Shinkansen seats. Only available on Hokuriku and Tohoku Shinkansen lines.
You can take any open seats in unreserved cars of any train on the departure date. (No departure time will be indicated on your tickets.)
The best seat type if your priority is the cost and are traveling during less-crowded season/time.
For further information and photos, please visit official page at http://www.jreast.co.jp/e/ticket/types.html