Adventurer's Union:

The Adventurer's Union is an international organization, recognized not only by the various governments but also by the World System itself. 

The Union originated as part of Ulrit Avalar, the first king of the Avalar Kingdom, gathered allies in the hope of culling the numbers of monsters that threatened the peace for the humanoids. Many years later, and the Adventurer's Union was born through an expansion of the already-existing Mercenary Union.

Mission:

The Adventurer's Union's goal is to accept and fulfill the requests given by the populace and the other Unions. The adventurers will do anything from hunting monsters, locating forgotten items, or guarding traveling merchants.

These Quests are ranked from G to A, with G being the easiest ones and A being the most difficult. There also exists S-Rank Quests, but rather than calling them more difficult than even the A-Rank Quests, the S-Ranks are better to be called rank-less Quests, due to their contents being too changeable to be assigned a real rank. It could also be in situations where one does not know how the Quest in question should be ranked.

The Quests are further divided according to their contents:

• Extermination Quests, where one needs to defeat a certain amount of monsters.
• Hunting Quests that asks for a specific material, be it from a monster or not.
• Bodyguard Quests, which revolves around guarding a specific individual(s).
• Exploration Quests that one examines forgotten ruins or other dangerous areas of interest.
• Odd Job Quests, which is usually for requests where someone of the public needs help with something not related to the other categories.

Rankings:

Including to the Quest Ranks, the adventurers themselves are divided into ranks. These ranks show the adventurer's talent and expertise with the job, and while they do not limit people to certain Quests, they are used as a standard for them. The rankings also tell how many Quests they need to complete within a certain timeframe without losing a rank.

The rankings go like this:

• G-Rank.
  • The fledgling adventurers. Can barely call them such.
  • They need to complete at least 5 Quests within a month.
  • They are recognizable due to their transparent ID-cards.
• F-Rank.
  • The real beginner-adventurer.
  • Can handle F-to-E rank monsters at least.
  • They need to complete at least 10 Quests that are rank F or higher within 2 months.
  • Have ID-cards that resemble wooden materials.
• E-Rank.
  • The novices.
  • A party of E-Ranks can fight against a small group of D-rank monsters.
  • They need to complete 5 Quests of rank E or higher within 3 months.
  • Their ID-cards are in bronze colors.
• D-Rank.
  • The more skilled adventurers.
  • Able to survive the attack of a C-rank monster.
  • Need to complete 5 Quests of rank D or higher within 6 months.
  • They got silver ID-cards.
• C-Rank.
  • The veteran adventurers.
  • Can hunt down C-rank monsters, and withstand weaker B-ranks even.
  • Need to complete 5 Quests of rank C or higher within 6 months.
  • Golden ID-cards.
• B-Rank.
  • One of the highest-ranking adventurers. Practically as important in their country as small-time nobles.
  • Can defeat even B-ranks if the need arrives.
  • They have 1 year to complete 5 or more Quests at rank B or higher.
  • Have platinum-colored ID-cards.
• A-Rank.
  • Literal heroes.
  • Can go toe-to-toe with A-rank monsters.
  • They can even say no to the king if they try to force a Quest on them.
  • They do not have to complete Quests within a certain period.
  • Their ID-cards are based on gems of their own choice.
• S-Rank.
  • Living Legends. A special rank granted to special individuals such as heroes from other worlds.
  • Like with A-Ranks, they do not need to complete Quests within a certain time frame.
  • Shares the same design on their ID-cards as the A-ranks.

10 Quests with a lower rank will count as a single Quest that is one rank higher.

To advance in one's Adventurer rank, one needs to complete enough Quests so that the Union Master in that area can allow them to take the advancement trial. The content of the trail changes with each rank.

P.S. The advancement from G to F-rank requires no trials. 

Carion's comment: While it's not obligatory, we also get requests to participate as mercenaries in wars.

Garami's comment: Guess not even a global organization can't run from their past.