Singapore to Hokkaido?

There is no direct flight between Singapore and Hokkaido. Nor is there any international flight from/to Hokkaido because Hokkaido does not have any international airport.

So you have to take a domestic flight after arriving in Japan.

We have 2 international airports, in Tokyo and Osaka (another one in Nagoya. But you don't have to mind it.). You need to take a flight to either one of those.

The international airport for Tokyo is Narita Airport. But it does not have many domestic flights. So I think it's better to go to Osaka and take a domestic flight to Hokkaido.

In fact, Hokkaido has more than 1 airports. But you can't choose many destinations from Narita. You must go to the domestic airport of Tokyo, Haneda Airport.

It's around 2 hours from Osaka to Hokkaido.
http://www.jal.co.jp/en/

Train? It could be 10 hours or more.

Hokkaido Airport

Does China Airlines fly out of SG? If so, you ought to be able to get a cheaper flight to Narita (Tokyo Int'l Airport) Then from there you could take a boat to Hokkaido. I hope that you know something about the weather in Hokkaido before you go there. Actually, the only warm month there is August. All other times the weather is either rather chilly or cold. Very heavy snow from late autumn until perhaps May.

ANA

Singapore 08:15 - Narita 16:20
Narita 19:00 - Sapporo 20:35
total:11 hours 20 minutes


Train

Narita - Sapporo : about 12 hours

refer these site

There is currently no direct flights from Singapore to Hokkaido. Your best bet would be to fly from Singapore into Tokyo or Osaka (or even Seoul, Korea) and then transfer to New Chintose Airport in Sapporo (biggest city in Hokkaido). The flight from Narita to New Chintose is a bit over an hour and a half.

The other way is to fly into Narita and then train to Hokkaido. I did that a few years back, stopping along the way to check out towns (Kakunodate, Amori, etc.). The train ride from Tokyo to Hakodate is about 7 hours (via Hachinohe). Then depends on where in Hokkaido you need to go, ie. from Hakodate to Sapporo is about 3 hours.