The Holy Grail. A grail that can grant any wish. To attain it, seven servants along with their masters fight against each other until only one remain. But, due to certain circumstances, the grail was corrupted and thus destroyed by Saber's Noble Phantasm. Now, the world was at peace as the Holy Grail War was no longer occurs or so it should be.
A world where fairies exist and lived in a different faction, a totally different world where the Holy Grail War takes place. Lies a castle contained treasures which every people resides in that world know. And, among of the treasures, there's a grail resembling the Holy Grail. The grail didn't appear just out of anywhere, rather it was created. By millions of code, every treasure was created by such complexity beyond human intellect. the one created it is the world itself, or the so-called game. The people who created the game have no idea how it suddenly appears, nor they could erase it.
To reach the castle itself you must cross hundreds of monsters, even if you managed to slip past, seven guardians will stop you from reaching the treasure vault. They have an inhuman reaction time, power, and agility. Even the admins or the so-called GMs cannot cheat its way through the castle. Just as they entered the castle door, the immortal object option is turned off, and disabled leaving them killable. Of course, they decided to change the approach, with max level and max stats. But, they're still killed.
Why is that? The answer is, they do not have the experience. The Guardian has their share of life-threatening battle where millions of battle experiences. And so, the GMs gave up. They cannot erase the place nor reach it, so they come up with an idea of making it an event for the players which the most residents in this world. They raided the place but to no avail as they cannot continue inside the castle.
The players notice the seven guardians have their different trait, the humongous human is called 'Berserker', as he easily wields a huge sword and kills the other player easily with a loud roar. The other was a magician class, she wields a staff and acts as the 'Berserker' support. The magic she uses was different than the Game mechanics. chant-less, as the players stupefied with her power. They call her 'Caster'.
The players only have met 2 of the guardian, they knew from the announcement made by the GMs that there are 7 guardians to be beaten. Until this day, the players kept pushing on to no avail.