Sanae is technically human, though she's got divine blood running through her—she's a distant descendant of Suwako Moriya, one of the shrine's resident gods. Her job at the Moriya Shrine sits somewhere between shrine maiden and full-fledged deity thanks to those inherited powers. When faith in the shrine dried up in the outside world, Kanako (the shrine's main deity) made the call to relocate the entire operation to Gensokyo, figuring youkai would be more reliable believers than modern humans.
She came in hot during Mountain of Faith, trying to strong-arm the Hakurei Shrine into submission so the Moriya Shrine could establish dominance. The problem was she badly underestimated how capable people like Reimu and Marisa actually were. After getting soundly defeated, Kanako and Suwako followed suit, but things eventually cooled down. These days the Moriya Shrine crew coexists peacefully with the rest of Youkai Mountain.
Her role varies depending on the scenario. In Undefined Fantastic Object, Kanako sometimes has her hunt youkai to build up her combat skills, while Suwako might send her after the Treasure Ship instead. Whichever mission she's on affects what secondary attacks she can use—snakes versus frogs.
By the time of Touhou Hisoutensoku, Sanae spotted what looked like a massive robot wandering around Gensokyo and went chasing after it. She ended up tumbling into a massive pit that led straight to Utsuho Reiuji's nuclear reactor, only to discover that Suwako had been behind the whole thing—she'd built Hisoutensoku.
Content compiled by AnimeList.moe from publicly available sources.
