Advancement in Underlight is not like advancement in other games. Advancement is an effort that involves social interaction and requires roleplaying.

In Underlight, levels are called orbits. Orbits can be obtained through a number of methods, from hunting NPC nightmares, performing quests given to you by other players, all the way to fighting other players. (Please note however, that fighting other players without an in character justification that coincides with your character's persona is considered "player killing", and may result in experience penalties or termination.) Upon reaching every 9th orbit, you will not able to advance further without seeking a player controlled teacher character and performing a customized quest to gain the next sphere.

All common arts are gained in the same way as spheres, however, they are slightly easier to obtain, although they will require that you complete a task of some kind.