It's an Ova from the same author as Kurenai http://en.wikipedia.org/wiki/Kentar%C5%8D_Katayama
Though some character, some actions and doings, the weaponry, the atmopshere and some yandere girls will totally remind you of higurashi, it's still unrealted. (but i guess theres no doubt that the author took all ideas from higurashi)
ohh and i saw someone posting a fitting description. Denpateki no Kanojo does in 40 minutes what most series can't do in 26 episodes.
It's a nice mysterious, involved and bloody psycho story about a mass murder and some allready insane people that get involved
check it out.