Osamu Nishi seems to have a heavy fondness for using the number 6 when anything numerical is mentioned, most often as the 666 combo itself, though she's just as likely to use 13 instead, all to make it extra blatant how the story is about demons in Hell (or the "Netherworld" as the story calls it). Examples of when the Number of the Beast pops up include:
- In Iruma's first year the school has 666 students in all 6 grades.
- The meeting of the three Demon Lord candidates takes place on the 666th floor.
- In the Anime, Sullivan does an OK sign with his three fingers curled. This is shown to represent 666.
- Also in the Anime, the demon school started its morning assembly in Episode 1 at 6:06. It would have probably been 6:66 if it was possible for a clock to actually be at that time.
- Azz stated he waited six hours and six minutes for Iruma on the first day of school.
- The Battler Rookie Hunt lasts for 66 minutes.
- Lied states that Kuromu's magnification power is 666 too much.
- The time when Kuromu's performance is meant to start in the anime is 6:06:06pm.
- Momonoki asks Clara to read the textbook from Page 66 during her class.
- The Demon King throne seen at the beginning of Season 2 and inside the Royal One have 666 on each side. The sixes on the observers right side are mirroring the sixes on the left. Though in the actual episode the 666's are facing the same way.
- 6.6 seconds is the limit for how long Romiere Ronove can stand being touched by another guy before he feels ill.
- The "Devi Dance Liberation" game rates scores with multiples of 6, from the lowest being 6 and the highest being 66666666. Iruma himself got an exact score of 666.
- Goemon stated he bought 66 copies of Kuromu's new song.
- Professor Balam made a picture book titled "666 Lil' Cerberus".
- During the SuKiMa skit for Season 2 Episode 12, when Opera is clearing some unneeded things for the Walter Park trip, two of the items were apparently the 66th and 96th (9 being and upside-down 6) most favorite snacks of Iruma, if Sullivan is to be trusted.
- Ameri's water park Date Plan was on its 666th revised volume.
- The Harvest Festival takes place over four days, or as Balam puts it, 6666 minutes.
- Eiko managed to survive to the last day of the Harvest Festival with exactly 666 points.
- When pointing out how boring Class A's performance idea is for the Music Festival, Ronove suggests that they sing 666 words of praises for him instead.
- During the Misfit Class' training for the Music Festival, Kerori orders the guys (sans Iruma and Purson) to yell "I'm so cool!" 666 times as their first assignment.
- The highest score the three judges of the Music Festival can give is 6 each, denoted by Oswell holding up three signs that combined read 666.
- Music Festival judge and former Thirteen Crown Amduscias is renowned for stalling enemy troops by performing a concert for 666 hours.
- The highest score of the First Year Music Festival is gaining three 6s from the judges. This is a rare event and considered fabled amongst the participants.
- The demonic currency, Vills (equivalent to Yen), are minted in denominations of 600, 60, and 6.
- Azz's birthday falls on June 6.
- The first event of the Evidol Games is a 66 meter sprint.
- Jackapo Insitute is a 66 story tower.
- Meta example: the duration of the preview for the anime's second season is 66 seconds.
- Back when Opera was a Former Teen Rebel, they apparently beat up 666 students by the time Kalego learned people were mistaking them for him.
- The Second Year Heartbreaker Competiton lasts only 66 minutes.
- There is a pillar of rock near the school. About half way up the wall, the stone gains an anti-magic field. Magic cast on it will only last 6 seconds.
