The Four Nexus Pillars

The Four Nexus Pillars are the foundation of Nexus as created by Professor Utake. They consist of four distinct domains, that function like the different "cells" that, together, form the structure of Nexus.

Each Pillar is guarded by one of Nexus' four admins, chosen by the Professor personally as his trusted guardians.

History
Professor Utake used to read a book he loved about a mythological fiction where heroic warriors fought against the gods. The book was written by the Professor's late wife, and it carried a very person message to him, since she wrote that book as a metaphor for the brave people who don't give up and fight against all odds, just like how she fought a disease for many years.

In the book, the obstacles of life, such as disability and disease, are represented by whimsical deities who reign over nature. They each gave ordeals to the warriors with disasters from nature - infernos, tsunamis, earthquakes and tornados. The four pillars are based on those deities and their domains.

Before leaving Nexus in the four admin's hands, Professor Utake developed four Nexus Pillar Deity cards - special cards that are at the same time four keys to the heart of Nexus and the strongest monsters to guard its order. Each of them is based after one of the book's heroes which fought against the natural disasters provoked by the deities' wrath.

Furthermore, they are a unique kind of card with a transparent frame. They have a Deck Master system: they belong neither to the Main nor Extra Deck and can be brought into play at any time, but if they are defeated, that means the owner's loss. The Pillar Deity cards are one out of two groups of special cards containing Nexus' technology - the other group being entrusted to the Professor's chosen heirs.

Admin
The Land domain is guarded by Eisuke Yamauchi, head of the regional police force. He commands different groups of enforcers, representing ["body parts of the law" such as "Eyes", "Right Arm", "Left Arm", "Brain", etc] - each with different specialties and tasks, that protect the community against criminal activities.

Function
The Land domain is linked to Nexus' [insert specific component/function here].

Pillar Deity
His pillar god is based on a hero from the book who swore to protect (someone). When confronted by the god of the land, he was tested with a series of powerful earthquakes that destroyed everything, making it seemingly impossible for him to protect that someone. The earth shook for hours, however, the hero didn't budge; he remained completely still and strong, and didn't move an inch from his place, protecting his beloved one.

Thus, the Land Pillar Deity is a monster that is one with the land, and once Summoned, he won't ever budge until his mission is over. As long as the user still has LP, the Pillar Deity can't be moved from his zone nor ever leave the field (so Kazuo's father fails to take control of it, and he can't get rid of it with effects either). It could be a Link Monster Summoned with 10+ materials.

Eisuke first Summons this card by using his Deck's unique gimmick to control 11 monsters. Later, a hacked version of this card could be used by someone, who Summons it using effects that force the opponent to swarm their field alongisde "Link Material".

Ocean
The Ocean domain is guarded by Rie Kamiya.

Function
The Ocean domain is linked to Nexus' [insert specific component/function here].

Pillar Deity
A Fusion Monster with lots of materials, just like the Land Deity. Rie Summons it using "The Evolution of Eons". When dueling against a specific opponent, said opponent "cheats" by using a Code Card or hacking a Pillar Deity (I like the latter better) and manages to get rid of Rie's "Deep-Sea" field and hidden monsters. As he does, the darkness is gone, revealing a Spell on Rie's field. Rie explains that she activated "The Evolution of Eons" on her first turn. She was sure that her opponent's skills weren't enough to defeat her, however, based on his confidence, she was expecting a dirty move such as hacking a Deity. Thus, she already set for the Summon of her own Deity - resulting in a clash of two Pillar Deities.

Core
The Core domain is guarded by Melody.