Star Birthmark

The Joestar Birthmark (ジョースター母斑) is a,five-pointed, star-shaped mark appearing in the region of the back of the left shoulder 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.

The origin of the Joestar birthmark is unknown, but within Phantom Blood onward, every member of the Joestar family by blood 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. Once Emporio Alniño enters the new universe, he discovers that Irene possesses the mark, helping him identify Jolyne as surviving in a new form.

Albeit they haven't been depicted visibly with the birthmark, it may be assumed that George Joestar I, George Joestar II, and Donatello Versus,all have the birthmark as well, as they are JoJos, Joestars, or members of DIO's progeny.

Like the original continuity, the origin of the birthmark is unknown but seemingly all members of the Joestar family by blood 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's 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,Nicholas Joestar and Holy Joestar-Kira

Trivia

 * Johnny Joestar is the only leading JoJo thus far not to have shown a mark in any medium.
 * Josuke wasn't depicted with the birthmark in Diamond is Unbreakable until the anime adaptation of the part.