Darkness Executives

The Darkness Executives (闇の執行部 Yami no Shikkōbu) are numerous shadowy figures that patrol the labyrinth beneath Riki's school during night time. They are the guardians of the secret treasure, and will do anything to dispatch ones who covet it.

Description
The Darkness Executives assume the form of humanoids wearing the school's standard uniforms and caps, with dark shadows instead of faces and hands. They are able to move around through shadows everywhere, and can fully materialize at night. Once shot, they melt into nothingness, leaving empty clothes.

According to Saya Tokido, the agent, the Executives are the hidden identities of the seniors of the school. Their leader is Shun Tokikaze, a mysterious man with a chalk-white mask and also the "Game Master" of this world.