Koyasan is not a normal day trip
Koyasan works best when you want a real change of rhythm: temple lodging, mountain atmosphere and a quieter night away from Osaka and Kyoto.
When it is right
Choose Koyasan when you want a slower night, a temple stay as an experience, and a trip long enough to absorb the extra logistics.
When to skip it
Skip it if the route is already dense, if Kansai has only one or two nights, or if the group mainly wants food, city evenings and easy logistics.
How to place it
Use Koyasan as a real pause, not as a hack between two rushed days. Osaka is often the easiest before-or-after base.
When to get personal help
Personal planning is useful if you want Koyasan without making the Kansai section feel fragmented.