This is going to be tricky. If you stuck entirely to public transportation, you could take a bus from Lake Akan to Kushiro or Kitami, then take the Senmo line (JR Hokkaido) from Kushiro to Shiretoko-Shari station, then take a bus tour or something. As you can see, it is highly roundabout, and you might be better off taking taxi from Lake Akan to Mashu station, then take Senmo line up to Shiretoko-Shari station.

In any case, you have to be highly mindful of train/bus connection times because the service in those areas is usually highly infrequent.

Thanks. Would there be any taxi driver willing to drive all the way from lake akan to Shiretoko? Can we negotiate a fixed sum in advance? It would be good if there is a private tour available.

There are a number of 1-day tours of Shiretoko Peninsula. But to fully enjoy its beauty it is best to drive there yourself as we did in 2 full days. Your time of visit is ideal for a self-drive road trip.

https://www.toursbylocals.com/Hokkaido-Shiretoko-NationalPark-OneDay-PrivateTour

https://www.viator.com/tours/Hokkaido/Shiretoko-Full-Day-Private-Tour-with-Nationally-Licensed-Guide/d5558-92136P178

If you want to use a taxi all the way, I'd recommend trying to reserve one in advance. Expect it to be quite expensive. Sorry i don't know about negotiation as I'm always fine with the default, using the taxi meter.

Thanks for sharing. Did you stay there for two nights? I am not sure is one night sufficient.

Last time I stayed in Shiretoko was in 2018 or 2019, and I think I stayed there for three or four nights. I stayed there for that length of time because I wanted to experience both Utoro and Rausu.

Utoro is the larger settlement of the two, and if you just want to stay there, I think two nights is fine. I feel that one night may be too rushed.