Cat Mercenaries is one of the most important Quests that needs to be done in-game. They will help your adventures along the way. Each of them has different skills that suits your needs.
You can unlock them at base Level 25, However, you need to finish each quest before you can hire them.

The Mercenary Cat level depends on your current base level, So the capabilities of your Cats depends also on how strong you are.

Cat Mercenary  Wasabi the Knight
Hire him inside Geffen City
Cost: 12,000 Zeny / Day or 72,000 Zeny / Week
Location on Map:

Cat Mercenary Maysa the Mage
Hire her inside Geffen City
Cost: 10,000 Zeny / Day or 60,000 Zeny / Week
Location on Map:

Cat Mercenary Po the Hunter
Hire him inside Prontera City
Cost: 10,000 Zeny / Day or 60,000 Zeny / Week
Location on Map:

Cat Mercenary Goro the Priest
Hire him inside Izlude City
Cost: 12,000 Zeny / Day or 72,000 Zeny / Week
Location on Map:

In case you want to hire the mercenaries again or accidentally kick them in the party.
You can invite them again by following this guide.

ROK ON!