Parallel World

In Jojo's Bizarre Adventure, the concept of Alternate Universes, realities or dimensions has been reoccurring theme periodically introduced throughout the later portion of the series. Originally conceptualized as the premise behind certain Stand abilities, the idea surrounding the existence of such universes has become one of the prominent features of JoJo.

Cream
Vanilla Ice's Stand, Cream is able to devour itself and its user to become a void that devours everything it comes in contact with. Vanilla describes it as a dimension of darkness, though he is unsure himself where exactly the objects are sent to. While in this dimension, Vanilla and his Stand are invulnerable to attacks.

The Hand
Similar to Cream, Okuyasu's The Hand is able to erase whatever space its right hand touches. Okuyasu states that not even he knows where the voided objects go, but it seems the objects are eliminated like an extremely sharp blade had sliced clean through them. This ability allows the normally short-range Stand extreme distance in its attacks, as it can simply remove the air between itself and a target to bring them within range.

Made in Heaven
Made in Heaven increases the speed or rate of the flow of time; achieved through its ability to control the gravitational forces of the earth, moon, and seemingly the entire universe (in reference to aspects of the theory of relativity).

As time continues to travel, the universe will hit a "vanishing point", and a new universe will be created, where everything repeats itself, according to "fate".The Stand's user may then alter the characteristics of the universe and the fates of the people in the recreated universe and create the perfect world they desire.

In the story, just after Enrico Pucci's death at the hands of Emporio Alnino and the Stand Weather Report, the universe completes a second cycle. In this renewed world, characters of seemingly very similar identities to Jolyne, Hermes, Anasui and Weather Report fortuitously gather in Emporio's proximity.

Dirty Deeds Done Dirt Cheap
President Funny Valentine's Stand, D4C allows different parallel worlds/dimensions to co-exist at the same time and/or in the same place. It also allows its user to visit these parallel worlds/dimensions and interact with them. Valentine travels by being closed between two objects, shown first by the use of a door against a wall. This method allows practically anything to travel between dimensions, including other people. Valentine takes advantage of this towards the end of Steel Ball Run to bring forth Diego Brando from Another Universe to aid him.

Steel Ball Run Universe
The Steel Ball Run universe (SBR universe) is an alternate world within the setting of JoJo's Bizarre Adventure. Its name is derived from the first story set in this new world, Part VII: Steel Ball Run. It encompasses the successor to SBR, Part VIII: JoJolion.

There exists a number of names, events, roles, personalities and relationships appearing in Steel Ball Run and JoJolion similar to those appearing in the original timeline. This article describes the theory, as maintained by a section of JoJo fans, that the SBR universe was created by the specific actions of certain characters at the end of Part VI: Stone Ocean.

Importantly, Hirohiko Araki has not stated whether the universe shown at the end of Part VI is the SBR universe or an altogether different one; and he indicates in the All Star Battle guidebook that Part IV and Part VIII are parallel worlds not linked in time or space.

Steel Ball Run
Part VII: Steel Ball Run, set in 1890, like Part I: Phantom Blood in 1880, follows Johnny Joestar and Gyro Zeppeli, characters with a number of ostensible similarities to Jonathan Joestar and Will Anthonio Zeppeli. Johnny is learning the Spin, a mystical power comparable to Hamon, from Gyro Zeppeli, an Italian expert in the art, like Will Zeppeli.

JoJolion
Part VIII: JoJolion is set in the year 2011 and follows amnesiac Josuke Higashikata, named for Josuke Higashikata of Part IV: Diamond is Unbreakable, as he searches for clues to his identity in Morioh, a town named after and located in the same place as the setting of Part IV. Along the way he discovers ties between himself and Yoshikage Kira, named after the primary antagonist of Part IV.

Alternate Counterparts
In the Steel Ball Run universe, there are many characters who reference characters in the original universe in some way; some closely, by the similarities to their roles in their respective stories, while others share only a few distinctive traits or experiences. In some cases, several characters share traits with a single character from the original universe, while others superficially similar to a previous character may harbour stark differences.

Morioh, the town serving as the base of Part IV, is similarly reincarnated in Part VIII.

The following represents a provisional list of those characters with obvious similarities.

Trivia

 * Other minor characters share small traits with past characters; for example, Andre Boom Boom demonstrates the ability to stuff his entire ear into his earhole, like Giorno Giovanna of Part V.