http://myanimelist.net/anime/18277/Strike_the_Blood
http://myanimelist.net/character/89423/Natsuki_Minamiya
A unique type of AR. It maybe tricky to understand how it works if you don't watch the some of the series.
The character is a witch with the appearance of a young girl who is a teacher at the main character's school.
In episode 16 a curse is placed on her that strips her of her "time" and memories leaving her with amnesia, a mentally regressed mind and a slightly younger appearance. This continues into episode 17.
http://animepart.com/strike-the-blood-episode-16.anime Episode 16
http://animepart.com/strike-blood-episode-17.anime Episode 17
Posted already in the TG area but there is a body swap between the male lead and his scheming childhood friend in episode 13.
http://animepart.com/strike-the-blood-episode-13.anime