How to go to Lake Kussharo & Mashu?

Hi guys,
So I'm planning to go with my friends to Hokkaido this December, and we want to go to Lake Kussharo & Mashu. But since we are going to use the public transportation, we have no idea how to access these two lakes.
Can you guys advise us on how to get to these lakes by using public transport? If possible, we want to go to these two lakes from either Asahikawa / Biei, since we are going there. But if it's not possible to access it from Asahikawa / Biei, we are open to any suggestions.


Why not rent car?
We are Indonesians. IDP issued in Indonesia can't be used in Japan because Indonesia isn't affiliated with the Geneva Convention.

Unfortunately, public transportation in the area is very bad. The basics are explained here:
https://www.japan-guide.com/e/e6805.html

Besides scheduled buses and trains, there are also sightseeing bus tours:
http://www.akanbus.co.jp/foreign/en/sightse/

And this could be of interest:
http://willerexpress.com/en/hokkaido-nature-pass/

There is a sightseeing bus for both of the lakes departing the Mashu station.

http://www.eco-passport.net/