There are a number of realities in the Siren games, all of which are very different. Some realities are false recreations of others, while others are not dependent on real worlds. There are realities spanning Forbidden Siren, Forbidden Siren 2 and Siren: Blood Curse.
Reasons for RealitiesEdit
There are deities in the Siren universe who cause a number of realities, some of which can be intentional or otherwise. Datatsushi, for instance, sent parts of Hanuda from 1976 and 2003 into a reality that combined both aspects of the town, as a result of the failure of the rituals in both eras.
However, Siren: Blood Curse offers two timelines that were created from actions from characters that differed from how their actions were supposed to play out in the timeline, therefore leading to the accidental creation of two timelines.
The Real World (Forbidden Siren 1 & 2)Edit
This world is the reality that humans live in in Forbidden Siren and Forbidden Siren 2. The real world is the dimension that we exist in, though not without the help of the supernatural. According to Forbidden Siren 2, there is a God who made the Earth, similar to the presentations of God in scriptures like the Bible. Supernatural entities do exist, but are relatively unknown to most of the universe's population. Deities like Datatsushi, Mother and Otoshigo have been present in Earth history, specifically Japan, and were even documented by the townspeople whom they visited, resulting in folklore myths surrounding them.
Incidents from 1976 up to 2005 have featured regular people plunge into a number of realities. To the outside world, they have vanished from the face of the earth. Of the people who have survived these experiences, only Harumi Yomoda returned to the real world, while everyone else were either dead in other dimensions or sent to other ones in the aftermath of the games.
The Real World (Siren: Blood Curse)Edit
The real world in Siren: Blood Curse is similar to that of the world in the first two games, except that this one exists in a completely separate universe. The only known deity that exist and have been dicumented is Kaiko. There are no documentations of the origin of the universe's creation, though it can be assumed that it may be similar to that of the first two games' universe.
In 1976, the town of Hanuda was sent into a a reality resembling it when the ritual to resurrect Kaiko failed, resulting in a landslide decimating the real town while its inhabitants were sent into this false reality.
In 2007, a TV documentary crew and a student entered Hanuda, but only Sam and Bella Monroe return to the real world, but in different time periods; for Sam, 1976 just after Hanuda's landslide, and for Bella, 600AD, eventually becoming Amana.
There are two versions of the False Hanuda Reality - there is the one featured in the original Forbidden Siren, and the one in Blood Curse. They share the same origin, created by a deity who crash-landed to Hanuda (Datatsushi in Forbidden Siren, and Kaiko in Blood Curse). The biggest difference in their origin is that the Forbidden Siren version is composed of the 1976 and 2003 versions of Hanuda, whereas the Blood Curse version is only made up of the 1976 town.
Both realities mirror their real counterparts, occupied by Shibito and any remaining humans. The objectives in the False Hanuda is to revive Datatsushi/Kaiko, allowing him to come back to full strength through the blood of Miyako Kajiro, who is referred to as the Bride of God. Ultimately, the ritual fails, and the gods of both realms are destroyed by Kyoya Suda/Howard Wright. Despite the alien-god's destruction, False Hanuda remains in place whil those who have not had the red water in their system return to the Real World. The shibito are eventually destroyed by Kyoya/Howard, following their promise to Miyako.
Similar to Hanuda, Yamijima Island underwent a process where the people in the island were transported to another reality in 1976, creating a fold in time around the island. The cause of this was from Kanae failing in her mission to release Mother, and when Kanae fell into the ocean with Shu Mikami during her escape. The time-fold allowed people from different times to be sent into this dimension when going to the island. As a result, the 1976 inhabitants interacted with those from 1986 and 2005. This reality was unstable due to the time-fold, therefore Mother's plan once freed was to exit it through Spider's Thread and reach the Real World. Eventually, this reality crumbled, sending Mamoru Itsuki, Ikuko Kifune, Soji Abe, Tsukasa and Yorito Nagai across dimensions.
The creation of this world is made after the defeat of Mother by Mamoru Itsuki and Ikuko Kifune. Upon her defeat, Mother - her avatars - were erased from the timeline. As a result, everything that transpired because of Mother no longer exists; Soji Abe, for instance, is no longer wanted by the police, as the avatar Ryuko did not exist, as well as her murderer, Yuri. It can be assumed that the 1976 disappearance of Yamijima island's population never occurred, or the Bright Win's vanishing.