The Forest Rest Shelter is a small pavilion/gazebo seen in the Elfen Lied series, serving as a bookend for the relationship between Nana and Lucy's more calm personality, Nyu, as well as the site of Yuka and Kouta's heart-to-heart moment. It is seen only in the manga, and like Maple House and the island containing the Diclonius Research Institute may have no real world equivalent. Even its probable location concerning the other sites, real and otherwise, is hard to determine being surrounded by woods.
In the anime, this structure is replaced by the Sasuke Inari Shrine and the Michibiki Jizoudou as a location where characters interact with one another. This change is in keeping with Director Mamoru Kanbe's use of and preference for the real Kamakura as a model for imagery.
Kouta and Yuka's intimate moment
For warmth, the two cousins and old friends move together, with Yuka working her way atop Kouta's leg since he is wearing pants and her only a skirt. Their closeness and confession of feelings towards each other lead to something short of a sexual encounter, with Yuka needing to take off her soiled panties while chastising an onlooking Kouta, who ends up seeing more than she wanted, despite or perhaps because of her efforts. When the rain stops, they find Lucy outside on the stairwell above them, who, pretending to be a more coherent Nyu, tries to bid them goodbye. Her explanations fall flat, and her nerve leaves her when she tries to tell Kouta it was she who killed his family when they were children. Once more becoming Nyu, Lucy leaves the area with Kouta and Yuka. The shelter seems to be near the stone stairwell that runs through Kamakura (perhaps to a greater extent with the fictional version than with that in the real world) but again is rendered indeterminate by the lack of direct landmarks and reference points. This moment is much more explicit in the manga than in its anime counterpart.
Nana finds that, after attacking Nyu on sight at Maple House, she is seen as the villain, even perhaps to Mayu, whom she had befriended earlier, and flees in anger and shame. As Mayu finds her, Nana reproaches her in both versions, but a critical difference emerges. In the anime, Mayu at this time is made explicitly aware of Diclonius and why Nana is angry at Lucy/Nyu. In the manga, Nana accepts that Nyu is not seen as Lucy by the others (though it would be a time before she fully saw this difference herself) and notes that Nyu does not register as Lucy to her Diclonius senses. Shortly thereafter, once more beginning to sense Nyu reverting to Lucy, Nana accepts Mayu's offer to come back to Maple House, where Lucy fades once more and Nana is eventually persuaded to stay and live in Maple House.
A Mercy Upon Nyu
After the horrific intrusion of the vile Unknown Man into Maple House, the grisly fate of Number 28, and the final bloody battle between Lucy and Bando, Nana retreats again to the shelter, once more feeling she brings bad things upon Maple House, which she now sees as her home and the people there as her family. As Mayu begins to agitate for their return home, events in the series, soon to reach a climax, overwhelm three of the main characters.
Despite almost being killed by Lucy, Mayu is still demonstrably reluctant to see the girl she has called Nyu as a murderer. It is at this time that Nana chooses to reveal her full story, and though no dialogue is posted in this sequence, the narrative as well as the looks on the girls' faces makes it clear that no details, however painful, are held back. Lucy, having reverted to Nyu after losing her horns to Bando's sacrifice to save Mayu, stumbled upon the shelter just as Mayu and Nana talk of how Nyu and Lucy are one and the same, and how Nana feels she must perhaps finally kill her. Perhaps this triggered a realization between the personalities, because Nyu flees from this revelation in terror. While Mayu protests on Nyu's behalf and Nana's moral well-being, Nyu finds a spot and begins to weep. As snow begins to fall and Mayu pushes for them to return with the shelter being rendered less than ideal, Nyu returns, only to face a furious Nana willing to strangle her, and being pushed further into rage when she spots cuts on Nyu's wrists, indicating she is suicidal and in fact wants Nana to kill her. Nana is pulled in several different directions morally, but chooses in the end to tell a pleading Nyu that she is not Lucy the killer. Even though Nana has resolved that she cares for Nyu despite Lucy, she still refuses to come home until Kouta, summoned by Wanta, declares her to be important to all of them. While this tender scene preceded by only a few hours the brutal home invasion of Maple House by the forces of Chief Kakuzawa, the rapproachment between Nana and Nyu could have influenced Lucy, set to leave Maple House for the last time, in charging Nana with the protection of their home and family.
Place in the series and real-life
The rest shelter is not seen again in the series after Kouta summons the group home. His hurried arrival there, and the fact that he had to be led there by Wanta, could indicate that the shelter is some distance away from Maple House, but not an insuperable distance. Yet it is not easily spotted out, indicating perhaps some distance from the main stone stairway. Its apparent architecture is not in keeping with Kamakura's Shogunate-influenced architecture, and being so apparently close to Jouju-in Cemetery, it calls into question whether so modern-looking a structure would be allowed to be built so near those hallowed and historic grounds. This could just be it's depiction in-series, or a reflection of the mangaka's skill at that time, which he himself has criticized.
Like with Maple House and the island housing the Diclonius Research Institute, it is not impossible for a place like this to exist; it merely seems unlikely, especlally given that it was replaced so easily by two different real-life structures in the anime. It serves a definite purpose in-story; on no less than three significant occasions, tensions built up in life at Maple House are vented therein, allowing the series' overarching plot to proceed from there on in. It is truly an open-air shelter on multiple levels.