They pretty much share the same mentality regarding nature and spiritual life, both being influenced by the supernatural. The overall atmosphere is also the same with incredible scenery and hauntingly beautiful music. The most simple things turn out to be miracles of life.
Both anime revolve around the spiritual aspect of nature and are rooted in Shinto beliefs.
Both deal with the supernatural and the relationships between humans and the world they inhabit.
Both are situated in an old Japanese era.
Both main characters looking after the spirits of nature.
Both are themed on plant, forest, animal, supernatural!
Both cover the spiritual world of old Japan, and watching Mushishi helps western people understand Princess Mononoke better.
A beautiful anime about relationship between human being and nature.
Mushishi and Mononoke Hime explore nature in a fantasy setting.
With their themes, both anime adapt a mystical background with ingredients of a tale involving characters that get themselves involved with supernatural beings. They also present a powerful background with a natural outlook of its nature.
The soundtracks are smooth ones that retain a serene-like feeling with minimal comedy. Character relationships are explored and the laws of nature with humans and beasts are also emphasized.
Both are filled with serene backgrounds and music and stress the theme of mankind's balance with nature and the spiritual aspects it possesses.
they both possess something soft and mature about them. supernatural, fantasy, and adventure. they have a very smooth transgression, get you thinking, and have a bittersweet feel to them.
Both share themes of nature, humanity, and the cycle of birth and death. Mononoke Hime has spirits of the forest, gods, demons... These are very similar to the mushi of Mushishi, with the main character of Mushishi also trying to find a balance between humans and nature, the same way Askitaka does. Both have gorgeous scenery and animation, with heavy emphasis on natural surroundings.
The atmosphere is very similar. Both deal with nature, the supernatural, and what is the very core of all life itself.
Both stories are about the coexistence of people and nature. Both using supernatural metaphors - spirits of nature - to tell the story.
They both have an incredibly similar world and atmosphere. An older time in the forests of Japan where there are themes of the spirits of nature and humans living in harmony.
Beautiful scenery and similar theme of respecting nature and humanity's place alongside it, even though nature can be dangerous and frightening.