- "The Altar of Hidden Evil has been opened. Beware members of Team Driller."
- - Official notice sent to Driller
The 'Altar of Hidden Evil' (Japanese: 隠された悪の祭壇, Hepburn: 'Kakusareta Aku no Saidan') is a fictional shrine hidden within Mineplex All Boys High School. The shrine was created under a hidden dungeon from Kenta Kazami, one the founders of Mineplex, and he sealed it after realizing it would cause trouble within the school. The sole purpose of the shrine is anyone who has an evil heritage can open it and their goal is to marry a girl from another school.
The shrine is also home to a basilisk, which was used to fend off students who try to rescue anyone trapped within it. The basilisk, which is mechanical, can respond to anyone who speaks to it and can accept orders spoken to it.
When Mineplex was founded in 1921, one of the founders, Kenta Kazami, wanted to have a hidden shrine within the school, so he created the Altar of Hidden Evil. However, he sealed it after the other founders told Kazami that the shrine would cause trouble within the school. He left and shortly after, he met Tsumugi Chikami, whom he eventually married and together, along with another couple, founded another school, being Minecraftia High School.
- "Don't blame me, Driller. The shrine hasn't been opened in over thirty years. The last time somebody was there, a youkai-born died. I ended up getting expelled for doing it."
- - Fred Fuchs, explaining it to Driller over an IM
Fred Fuchs opened the altar during his fourth year at Mineplex All Boys High School. With it, he used the shrine to marry Emenbee All Girls High School student Hanayo Katsuragi. Katsuragi would end up becoming Hanayo Fuchs, and in order for Fuchs to get Katsuragi to fall in love with him, he used a Love Potion to make this happen.
In 1988, Hanayo had Jack Fuchs, who would eventually become Takumi Hearthcliffe. Katsuragi died shortly after his birth due to the fact that she had immersed herself in dark magic from Love Potions.
- "Wait a minute, didn't Hearthcliffe try to marry Kagami!? If he did, then my entire family's life would be completely destroyed."
- - Kisumi Ochiai, to Driller
The shrine was opened again by Fuchs' son, Hearthcliffe during his fourth year as well in December 2006. This time, Hearthcliffe's goal was to use it to marry Kagami Ochiai in order to prevent Driller from marrying her. To make things worse, Hearthcliffe used Polyjuice Potion to take on the form of Driller and to carry this operation out.
With the basilisk causing trouble, many students were frozen solid from its projectiles. Many students from Minecraftia High School were affected after they saw it on social media or its reflection.
However, Hearthcliffe decided to hold his wedding with Ochiai on Prom Night. However, the engagement ring he used to get Kagami engaged was actually his class ring, which he transformed into a Horcrux. During the wedding, Driller broke inside the shrine to rescue Kagami. When Driller found out that Hearthcliffe was using Polyjuice to impersonate him, he shoved a bit of milk to make the effects wear off. With Hearthcliffe angry after wasting all of his Polyjuice, he unleashed the basilisk with Hearthcliffe's order to take down Driller. Knowing that being hit with its projectiles would be fatal, he started running from it. At that time, Yumi came in with Honoka Akimoto's Lightsaber that Driller can use to fight the basilisk.
With Driller getting ahold of the lightsaber, he was able to fight the basilisk without any trouble. With enough strength, he kills the basilisk with it and uses the lightsaber to destroy the Horcrux. This, in term, freed Kagami who was about to become imprisoned by Hearthcliffe.
The shrine was opened a third time by the couple of Madoka Fujima and Hideki Katayama. This time, they went inside to retrieve more basilisk fangs for Driller, as he needed them to destroy Hearthcliffe's final Horcrux. Once they got inside, they broke off multiple fangs in order to destroy the horcrux.