The Jinshin War was fought between Prince Ōama and his nephew, Prince Ōtomo, over succession to the throne. The mountainous region of (in modern-day Nara Prefecture) served as a strategic and spiritual refuge. Yoshino was considered a wild, liminal zone—close to the "other world" of the gods and the dead.

You're referring to "Yotsuba&!" (also known as "Yotsuba mago" in Japanese)!

Historical records regarding Yoshino Mago are sparse and often contradictory. The name "Yoshino Mago" literally translates to "Grandchild of Yoshino" (or sometimes "Yoshino's Whip/Wicker"), but most scholars interpret "Mago" here as a title or a nickname referring to a low-ranking mountain warrior or yamabushi (ascetic monk).

– When Prince Ōama’s forces were outnumbered, Yoshino Mago is said to have used kuji-kiri (nine hand seals) to summon the spirits of fallen warriors from the misty peaks, creating the illusion of a massive army and causing enemy troops to flee.