School Days: Magical Heart Kokoro-chan
Japanese title: School Days ～マジカルハート☆こころちゃん～
Type: OVA
Source: Visual novel
Episodes: 1
Status: Finished Airing
Aired: Mar 26, 2008
Duration: 24 min
Rating: R+ - Mild Nudity
Studios: TNK
Producers: Avex Entertainment, Marvelous Entertainment, Lantis, Pony Canyon
Licensors: Discotek Media
Genres: Comedy, Ecchi
Themes: Parody

Originally an April's Fool in 2007, this one episode OVA is a spin-off of the School Days game by 0verflow, and shows Kokoro Katsura, the little sister of one of the main characters, from her other side. A mahou shoujo out to save the world, or something like that.

(Source: AniDB)