•In The Vampire Diaries Universe, The Other Side was a dimension of afterlife also known “Supernatural Purgatory” created by Qestiyah,
The show canon said all creatures considered supernatural all goes to The Other Side:
•Witches
•Doppelgangers
•Werewolves
•Originals Vampires
•Supernatural Hunters
•Vampires
•Hybrids
•Human(Gilbert Ring)
These are all supernaturals creatures who inhabited over there for 2,000 years.
The Prisons Worlds are technically alternate pocket universes/dimensions where they repeate everyday on temporal loop(Everything like object, foods and celestial events reappers on 24/1).
In May 10th 1994, the Other Side still existed and the Gemini Coven(A coven of witches) did a banishment and creation spell to ceeate a prison world for Kai Parker.
At some point of time, as supernatural siphoner witch Kai Parker killed himslef and died. The question is what happened to his soul? Did he go to the Other Side due being supernatural before he came back life in prison world?