I did this as a full one day hike whilst staying at Anbo.
Get an early start; you'd want to be up and on the road by sunrise at the latest.
I hired a guide (Jen from Yakushima Life) at 16,000yen. When you consider buses are sporadic at best, and taxis will drop you off (and pick up!) at the hike entrance at 7,000yen each way, this was an excellent value proposition. Breakfast, lunch and a knowledgeable and engaging guide as well.
Whilst the trek was long, it was not necessarily treacherous. I was fortunate to have clear skies almost all morning, so avoided having to scramble about on wet rocks.
You'll need proper gear (waterproof pants and jacket, good shoes) as the weather can change quickly and sometimes harshly. Ketitai toilets are a must. The water on the mountain is fresh and potable, so you needn't take a huge water bottle, as streams are fairly common and can be replenished.
A return day hike would reasonably take 8-10 hours without pushing yourself. You should have a degree of fitness, as there are some steep incline and short rope climbs involved.
Own or manage this property? Claim your listing for free to respond to reviews, update your profile and much more.