Rebirth skills, also known as "RB skills", are skills that are unlocked after rebirth.
Each character has 4 rebirth skills that are based on their existing skills, with the 'True' prefix in their name. These skills can be learned immediately after rebirth.
Despite the 'True' prefix in their names, true skills are not necessarily superior in every way to their regular counterparts, and might be completely different in some cases. For example, Eir's Bead of Healing creates a bead which revolves around her and heals nearby party members, while her True Bead of Healing fires healing beads at distant party members. Similarly, Dark Eir's True Blade of Chaos has more damage and width than its non-rebirth counterpart, but less range and more cooldown.
75s, ultimates, and some custom skills may also be known as rebirth skills, as they require rebirth.
Rebirth skills can be disabled in PVP.