Level

Level is an attribute of Characters. Level determines a character's maximum HP along with the individual character's intrinsic Life Force Factor, and also improves damage with all Weapons. Level is increased by gathering the Exp Orbs which are given off by defeated Demons.

Effects of Level
Level multiplies both HP and all damage by the same factor.

While there is no upper limit to level or the benefits of level, it still experiences diminishing returns: the multiplier is given by (level + 17*sqrt(level))/18. This is a different multiplier than that used for Tiers, in which the multiplier has an upper bound.

Requirements for Level
In contrast to Tier, all Exp Orbs count towards Level. The total number of orbs required to reach a given level is given by level2/2 + 81*ln(level/8 + 1), rounded to the nearest integer. This formula is in fact reused for tier.

Level vs. Tier
Levels and tiers are parallel progression systems. Each character has one overall level, but has a separate tier for every weapon. Levels affect HP and damage but do not effect charge speed, while tiers affect damage and (for the majority of weapons) charge speed, but not HP. While both levels and tiers are unlimited in principle, each level continues to provide an incremental benefit, however small, for arbitrarily many levels, whereas the benefits of tiers have an upper limit.