From MangaHelpers:

In this manga, the famous male onmyouji Abe no Seimei is actually a female college student, Abe Akirako, who was sent back in time from the Heisei (present-day) period to the Heian period (794-1185)! She doesn't really have any skills, but she uses the random modern stuff she had with her for the time slip to support her reputation as the genius onmyouji. Just after her time slip, she is picked up by Fujiwara no Michinaga, who takes her in (in her male, onmyouji identity) and becomes her ally in this new time period. From Abe's point of view, she's gone from NEET to elite, so maybe the Heian period isn't such a bad place to stay!