Guilds in Gekkeiju Online™ are character class professions that teach skills and possibly spells to players. Each Character Class has a wide range of different guilds that the player can join.
Joining of a guild is possible after reaching level 10. At level 10 players start gaining so called Free Levels which can be used to either advance in a guild or to join a new one.
Before being able to freely join all the Character Class' guilds the player needs to maximize the so called Class Guild. Each Character Class has its own Class Guild which teaches the basic skills (and spells) to the player. These Class Guilds take 10 Free Levels to maximize so at level 20 players are able to join other guilds. Class Guild-trainers can be found in most towns.