Level 100. From the moment an Adventurer signs the contract and receives their system, the level cap will be placed upon them. No matter how hard they try, or methods they use, the limit will remain in place.
No one knows what the creators of the system thought of when they placed the level cap, or why they assigned 100 as the threshold. There was only the truth and the simple truth of accepting that fact.
It was one of the reasons why Guilds became more prominent. Some beasts are too powerful to be defeated by a single Level 100 Adventurer alone. The limits to their capabilities hinder their power, causing them to be unable to reach greater heights.
Rumors has spread throughout centuries, that a certain artifact could break the level threshold. Adventurers from all over the world sought for this item, desiring its powers. But no one succeeded.
Nobody, until the first owner.