Star Birthmark

The Joestar Birthmark (ジョースター母斑) is a distinct, five-pointed, star-shaped mark appearing in the region of the back of the left shoulder or close to the neck on all JoJos or individuals of or in certain ways connected to the Joestar bloodline.

It was introduced in Stardust Crusaders and becomes important again in Stone Ocean. The anime incorporates the birthmark earlier, depicting Jonathan Joestar and Joseph Joestar with it. It resurfaces in the second continuity within JoJolion.

Original Continuity
The origin of the Joestar birthmark is unknown, but within Phantom Blood onward, every member of the Joestar family bears the birthmark. At the end of Phantom Blood, Dio Brando murders Jonathan Joestar and takes over his body. Through this process he inherits the birthmark but rests at the bottom of a sea for a century. Later, in 1983, DIO reawakens after escaping his coffin. He travels around the world and impregnates multiple women with his children, notably Giorno Giovanna, the protagonist of Vento Aureo.



The birthmark is only formally introduced in Stardust Crusaders by Joseph Joestar to Jotaro Kujo. With DIO's reawakening, the special connection he gained through Jonathan's body puts Holy Kujo in danger, so they set out to destroy DIO. A few years before these events, Joseph Joestar has an affair that results in Josuke Higashikata; who as a part of the Joestar family, inherits the birthmark.

In Stone Ocean, the birthmark becomes integral once again. Jotaro Kujo's daughter Jolyne Cujoh faces off against an eccentric priest, Enrico Pucci. During the events of Stone Ocean, Pucci fuses with the Green Baby and gains the birthmark, as the homunculus partially originated with DIO's Bone. His brother, Weather Report also receives the mark; and as twin brothers, they connect and affect one another in the same way DIO does with Joseph, Holy and Jotaro in Stardust Crusaders.

At the end of the story, Emporio Alnino enters the new universe where he discovers Irene, a woman nearly identical to Jolyne, shockingly possesses the mark.

Characters of the original continuity's Joestar family who were not depicted with the birthmark include George Joestar I, George Joestar II, and Donatello Versus.

Steel Ball Run Continuity
Like the original universe, the origin of the birthmark is unknown but seemingly all members of the Joestar family bear it. Johnny Joestar's is never shown but Lucy Steel is aware of it. His grandson, Joseph Joestar bears the birthmark, and his Stand protrudes out of it.

Later on, in JoJolion, the protagonist Josuke Higashikata bears the birthmark through seemingly unknown means. It is eventually revealed that he inherited this birthmark through a Locacaca fusion of Yoshikage Kira and Josefumi Kujo. Kira's sister, Kei Nijimura, also bears the birthmark.

The Joestar birthmark plays into Josuke's usage of his bubbles and the Spin, as the bubble comes out through it.

As well as Johnny Joestar, characters of the new continuity's Joestar family who were not depicted with the birthmark include George Joestar II, Nicholas Joestar, George Joestar III, and Holy Joestar-Kira.

Trivia

 * Both Jonathan and young Joseph weren't depicted with the Joestar birthmark in their respective parts due to the concept of the Joestar birthmark not being introduced until Stardust Crusaders. Jonathan's was later included in the Phantom Blood film, 2000 Stardust Crusaders OVA, and the anime adaptation. Young Joseph's birthmark was included in the anime adaptation as well.
 * Josuke also wasn't depicted with the birthmark in Diamond is Unbreakable until the anime adaptation of the part.
 * An artwork in the Hirohiko Araki JoJo Exhibition 2012 shows Lisa Lisa with the birthmark, despite being from a different family and not being biologically related to the Joestar Family.