The seven mysteries of Kuoh academy

"You underestimate the Seven wonders of Kuoh, miss Kurama."

- Ren to Kurama, talking about the remaining mysteries

The Seven Mysterious wonders of Kuoh Academy(駒王学園の七不思議; Ku-ō gakuen no nanafushigi); or simply The Seven Mysteries, is a recurring secondary chain of events in Highschool DxD: Яe-birth. First introduced during the events of Volume 5, for the next volumes up to the 7th, it'd take a secondary stage between the events of the "Miyama Runaways" Arc and the "Devil/Vampire peace conference" Arc.

Overview
First introduced during the events of the "Miyama Runaways" arc by Ren, the Seven Mysteries of Kuoh academy are seven urban legends talked about among the students of Kuoh academy, and may or may not be a dangerous threat for the devil/Vampire peace conference that would take place in the school. To avoid any possible future problems, Ichijou, Ren and several others members and staff of Kuoh academy partook in a search for said mysteries to be sure they won't cause unnecessary ruckus in Kuoh's schoolar life.

1th wonder- The Mysterious Locker Room Lights:

 * Mystery: The first Mystery discussed during the events of ch. 34, it is a about a strange phenomenon in which, for some mysterious reason during days in which there are no after-school trainings, bright lights come out of the Kendo club's locker room, Known as the "Mysterious Locker Room lights"(ロッカールームの奇妙な光; Rokkārūmu no kimyōna hikari)
 * Truth: It turns out, a pair of grey-skinned, slim and tall aliens hide their human-skin disguised after a certain period of time on Earth passing students of Kuoh academy. The said bright light comes from their mothership using a transportation ray to take them back.

2th Wonder- The Ghost of the second Floor:

 * Mystery: Students discuss that, during lunchbreaks, ghosts apparently play pranks on students of the second year by lifting objects and drop them, making chilling noises and scaring whoever is unlucky enough to cross paths with said ghosts. Students outogether avoid the second floor in order to also avoid said ghosts of the second floor(二階の幽霊; Ni-kai no yūrei).
 * Truth: There is no ghosts in the second floor. In reality, those are indeed pranks, but they origin is the prankster tranferred student of the class 1-B, Mizuki Kyouka, using her psychic powers out of boredom in order to scare fellow upperclassmates. As soon as she was revealed, such phenomenons stopped.

3th Wonder- The prankster Imp:

 * Mystery: It is said there's a strange, small creature, believed to be an imp, that runs around Kuoh academy laughing and bumping into students. When someone tries to catch it, it mysteriously dissapears on the next corridor without lasting traces. It is known as the prankster imp(いたずら鬼; itazura oni)
 * Truth: Salvatina Veritas, as it turns out, is the said imp, running around searching for the current red dragon emperor, Ichijou Tsukino, and due to her typical childish euphoria, ends up bumping into several students, and using her vast knowledge in senjutsu to avoid being seen.

4th Wonder- The monster of the swamp:

 * Mystery: Students claim that, at nights of full moon, they'd hear a strange noise coming from the abandoned pool next to the kendo club. Said pool would actually be the home a large, foul-smelling and violent swamp monster(沼の怪物; Numa no kaibutsu) that attacks people fueled by the forces of the moon.
 * Truth: The swamp is actually a sentient moss that can produce tentacles out of it's mass, trying to obtain as much as energy and light coming from the reflect sunlights of the moon in order to bloom, since Desmond Hellsing, the prime minister of the Vampire Empire, used a special spell to cloud Kuoh city in order for his compatriots to safely travel from Romenia to Japan.

5th Wonder- The Mysterious Student of class 2-B:

 * Mystery: Rumors says that a student from class 2-B emanates a strange energy around him, and such energy, during classes and lunchbreaks, tends to cause interference in nearby mechanical or eletrical devices. It is known as the Mysterious student of class 2-B(教室2-Bの奇妙な学生; Kyōshitsu 2-B no kimyōna gakusei).
 * Truth: The said student does exist named Satoru Nekomecha, a tin-can-shaped robot with cat-ears that calls himself a nekomata. The said interference is a strange wavelength antenna located on top of his head, which causes said waves of interference, which he calls his senjutsu arts.

6th Wonder- The evil dark blob around the Headmistress's office:

 * Mystery: Students have claimed that a mysterious, amorphous ball of pure blackness wonders around tin front of the office of Kuoh Headmistress Shizuka Morimoto, carrying with itself a heavy, malevolent aura, and it dissapears suring lunchbreaks. It is rumored that is an ex-boyfriend of said headmistress hauting her during the day, taking the form of a black blob(黒いブロブ; Kuroi burobu)
 * Truth: The one waiting outside it's actually the shy, cute half-grim reaper hybrid Whiswain, that due to her shyness, is unable to gather enough courage to enter the office during classes, and when lunchtime breaks out, she hides out of fear from other students, repeating said process over and over again.

7th Wonder- TBA

 * Mystery: Unknown, TBA.
 * Truth: Unknown, TBA.

Trivia

 * The Seven Wonders are based around the japanese concept of seven summer mysteries, in which students partake in seven courage tests in order to 'cool off' during the heat of summer.
 * As in turns out, three out of the seven mysteries end up as recurring characters in the Fanfiction.
 * All of the wonders ended up as being a complete, out-of-nowhere subject even in canon rules in the Universe in Highschool DxD, including aliens, spirits, robots and psychics.