Nightruth: Yami no Tobira

Shinya Izayoi is not your average high-school student. He's knowledgeable in black magic, wears a ring that summons a magical sword, and is part of a group of students that investigates paranormal activity. Strange events such as spontaneous combustion have been happening recently, so Shinya and his (mostly cute and female) friends are drawn in to get to the truth of what's happening.