Rebirth is the process by which a soul enters the developing body of an unborn child and begins a new life. Usually they aren't capable of determining their sex or species, although personal preference and identity is believed to play at least some part in it. Some people are consistently born as one particular sex or species, while others vary wildly.
Typically, the new being has the same Talents as the old one, but they have been known to change and shift over the rebirth process. Sometimes they grow weaker or stronger, while other times a person may gain or lose entire Talents. For example, Azale gained Motion Magic during his last rebirth, which he had never had before. But as a general rule, Talents tend to remain relatively consistent.
The personality of the new person can be very different, depending upon their experiences.[1] Memory does not always remain constant during rebirth. Under normal circumstances, the infant will not remember their past lives at all, but may sometimes slowly recover their memories, bit by bit, through dreams and flashbacks, until adulthood. If they reach adulthood without fully recovering their memories, chances are they will not recover them on their own, and will need the assistance of memory magic. Mind Magic alone is capable of restoring memories to some extent, but to recover ones that have been completely lost, Time Magic is needed as well.
Although temporally non-linear rebirths were possible up until the War of Planar Dominance, Sharina Kell put a stop to that when she briefly took control of the universe. She considered being born into the past was confusing and extremely annoying, as she had had to experience the Planar Wars twice because of it.
When Jez'kai took over the Elkandu Universe, he ended rebirth entirely, and had souls sent to an afterlife instead.