Opassa Beach is an enigmatic coastline found on the southwest corner of the El Nido island. A scenic and beautiful stretch of sand, it was often visited by residents of Arni. Specifically, Serge and Leena often met there. In 1010 A.D., while visiting the area, Serge was attacked by his father Wazuki and brutally drowned; this caused Arni village to post warning signs around the area and forbid entrance to young people. Later, in 1020 A.D., Kid traveled back through time and rescued Serge, effectively causing the Home World dimension to come into existence and split off from the main dimension, Another World. As a residual effect, a connection was retained between the two dimensions at Opassa Beach, allowing the missing piece in Another World to venture to that dimension by utilizing a dimensional distortion (in all likelihood, Opassa Beach was probably specially constructed or enchanted to have this effect by Belthasar). Belthasar named the distortion Angelus Errare - Where Angels Lose Their Way. The Gate went unused until 1020 A.D. in Home World; on a lark with Leena, Serge was engulfed by a wave and slipped into Another World. Much later, he was told by Kid that her Astral Amulet would allow him to come and go as he liked between dimensions; he utilized this capacity to retrieve Hydra Humour for her. Party members could also come with him to the other world, provided they were in close proximity. When Serge switched bodies with Lynx, the distortion stopped functioning as it did not recognize his body.
Somehow, the destruction of the Dead Sea reactivated this capability, and Serge was free to travel between dimensions once more. The final purpose of Opassa Beach came at the end of his quest, after Terra Tower emerged and was infiltrated. Belthasar gave Serge a Time Egg to use at a special temporal distortion at Opassa Beach which would allow him to enter the Darkness Beyond Time and challenge the Time Devourer. This distortion appeared purple (Angelus Erarre appeared green); the Ghost Children also appeared on the beach and encouraged Serge to finish the effort and free Schala. He held up the Time Egg, and disappeared to the darkness. Later, he woke up on the beach, though at the time of his original crossing the dimensions.
The Angelus Errare may be a pun on the American City, Los Angeles. While in Spanish the term translates to "The Angels", it does seem to have a tongue-in-cheek meaning in English: "lost angels" or "loss of angels". Also, the scenic positioning of the city resembles Opassa Beach.