Since you won't find a lot of information on climbing Mount Yôtei (not in English anyway) and because of the incredible experience, this rather lengthy post with lots of images.
Standing at almost 2000m, mount Yôtei (Yôtei-zan in Japanese), nicknamed Ezo-Fuji for its' resemblance of Mount Fuji is a dormant volcano in Shikatsutoya National park on Hokkaido. It is possible to hike to the top and come back in one day. Going up will take anything from 5 to 9 hours, depending on how fit and well equipped you are; going down a mere 2 hours. Alternatively, you can go up, stay in the hut just beneath the top and go back the following day. That is what I did and I can whole heartedly recommend this option, you will be rewarded with a beautiful sunrise. Whatever you choose, you will have to be in a very good physical condition and you should be prepared to the utmost. I choose the north-west hike (from Hangetsuko camping) which is pretty straight forward (just follow the footsteps.)
First, this is one though nut to crack. I have hiked 4000m+ mountains that are easy in comparison. It doesn't show if you look at the photo's but the ascent is steep with ascent percentages of well above 40%. The snow was not helping very much (and sometimes I sank knee-deep into it.) My physical condition is very good but I had to go very deep (to put matters into perspective, fitbit data showed afterwards that I went well above 180 bpm heart beat!) My advice is, if you're not 100% fit, don't do it...
Second, and this may vary according season of course (I went end of april), bring lots of clothing. Once the sun was setting (around 17h00), it was chilly, and the wind made matters worse. When the sun was under, it didn't take long to begin freezing (and not just a little: ice and snow grew rapidly on the few tree branches that were there...) I had six layers (of which a thick woolen Icelandic pullover and a fleece sweater) and that was barely enough. Don't forget gloves! Some protection for electronic devices would be wise too: my camera was completely covered in rime overnight and completely froze up.
Thirdly (and probably most importantly), check for the weather conditions, as these change rapidly on a mountain. I was lucky enough to go on a sunny day, but I can't imagine what it would be in fierce weather. Very important: check the risk of avalanches if there is still snow on the mountain.
Lastly, bring enough food and drinking water (I had 4 liter and 2 kilo food - mostly fruits and nuts.) As with most hikes, you will also need a compass, a good knife, a lighter,... If you are staying in the hut you will have to bring with you anything you might need.
With all that said, it was an incredible experience for me and one of my best hikes ever. You are as close to nature as you will ever be and you just have to worry about you and the mountain. I feel the pictures just don't do any justice of the hike, but I am going to post them anyway as it is the only thing that I can show for. The thing I regret most was that the camera froze at night and all I got was a blinking battery. As such, no photo's from an incredible sunrise...
Images taken May 2017, Pentax K-5 + DA 20-40 Limited and DA 15 Limited