天岩戸, the Lightless Vault







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RPC-257, prior to the installation of Outpost-089-A.


Registered Phenomena Code: 257

Object Class: Gamma-Purple (Utility)

Hazards: Aggressive, Destabilization, Extra-Dimensional, Grouped, Immeasurable, Temporal

Containment Protocols: The mainstream and non-anomalous counterpart of RPC-257 located in Takachiho, Nishiusuku District is left as-is in order to serve as a non-anomalous tourist destination, drawing off any possible interest in seeking out the actual phenomena located █km away at [COORDINATES REDACTED]. Satellite photography must be doctored to conceal its existence as well as that of Outpost-089-A.

Under the guise of private property, no printed or digital maps are to include any trace of the unmarked road leading towards it. RPC-257 is enclosed within a fenced 1km radius as well as being fully surrounded by the walled enclosure of Outpost-089-A, both perimeters being patrolled on an hourly basis. Any hitchhikers and explorers who reach the external security booth are to be turned away, and those who somehow pass through the fenced perimeter are to be detained, threatened with police action, and released. Trespassers who somehow reach Outpost-089-A must be amnescitized before being released.

Alongside housing Authority personnel, Outpost-089-A must also be stationed with no less than three (3) Authority-sanctioned Onmyōji responsible for maintaining and inspecting RPC-257-1. Beyond the shrine disguise for the cave opening leading into RPC-257, entry into RPC-257 has been reinforced with a series of blast doors warded with numerous Shinto charms. A security checkpoint and a final reinforced blast door is installed deeper within, 100 meters before RPC-257-1. In event of a breach, personnel within the checkpoint are to seal all blast doors and evacuate stations by utilizing the emergency elevators. Should the elevators fail, personnel may utilize the automatic rappeling cables to be drawn up the shaft.

Expeditions into RPC-257-2 require the joint authorizations of Site-089's Senior Researcher Junichiro as well as Site Director Hiroi Genichi. The expedition team must consist of experienced spelunkers and at least one specialist in Japanese cryptozoology. The expedition is to wear sound-dampening equipment and utilize night vision systems. Expedition members are to not raise their voices beyond 5db and must not shine a light upon entities for longer than 5 seconds. Direct physical samples of specific entities may be taken only with written pre-authorization by Sr. Rsc. Junichiro.

Any potential reanimation incidents must result in the immediate termination of any ongoing expeditions, especially if said reanimation incident includes any form of assault upon any expeditionary member. RPC-257-1 should then be reinforced through the aid of Authority-sanctioned Onmyōji (Based on instructions gleaned from surviving Hidden Sun documents) and not to be passed through for a minimum of 1 week. The aforementioned Onmyōji are to also inspect RPC-257-1 on a weekly basis and note down any developments to its existing damage.

Description: RPC-257 is a location in the Miyazaki prefecture of Southern Japan. It is formerly the dwelling grounds of the Hidden Sun Clan1, effectively replaced by Outpost-089-A post-discovery (see discovery log below). Prior to their destruction, the reclusive Onmyōji2 of the Hidden Sun Clan charged themselves with the caretaking and maintenance of RPC-257-1 as well as maintaining an environment of utmost secrecy, turning away and preventing all visitors from approaching RPC-257. Lastly, the clan mystics would conduct rituals to regularly ensure the capture of anomalous Japanese cryptids and their containment within RPC-257-2.

Beyond the cavern's entrance, geological analysis of the cavern walls reveal partially melted and reformed stone, aged magma formations and obsidian formations dated to have been created roughly two thousand years ago. The pattern of obsidian formation suggests brief initial exposure to an intense heat source, followed by a cooling period, then re-exposure. This phenomena is allegedly explained by a well-known legend within traditional Japanese mythology: RPC-257 was supposedly the temporary residence of a prominent divine mythological figure who self-imposed exile upon itself during a supposed altercation with similar beings.

The cave descends down a gentle incline without any anomalous traits until RPC-257-1 is reached. RPC-257-1 is a floating brass disc measured to be 0.67m in radius with a thickness of 55mm and an estimated weight of 24kg, engraved with Shinto script throughout its entire surface and suspended in the middle of the air. The air surrounding this medallion is noticeably dense, with personnel describing the need to "wade" in order to pass through and descend deeper. Based on survivor testimonials, RPC-257-1 was originally in pristine condition prior to discovery. It now sports fissures and cracks running along its surface caused by a bladed object, with extensive marring rendering at least one-third of its frontal engravings illegible.

Beyond RPC-257-1 is an anomalous zone labeled RPC-257-2. While above-ground radar charting suggests RPC-257-2 being a single large cavern, personnel observed via beacon tracking are seen to float across the open space of the cavern, then vanish upon moving past the end of the seismological charting map.

RPC-257-2 consists of a single main tunnel that continues onward, while being flanked by openings leading to side-chambers. Regardless of their size and closeness towards each other, these openings always lead into separated chambers, even if two adjacent openings should naturally result in their chambers being merged into a single room. Each chamber acts as the housing location of a variable number of a single species of anomalous Japanese cryptid entity, partially desaturated of colour and suspended in a form of temporal stasis.

Shining a light upon said beings for an extended period of time or creating prolonged loud sounds can cause these entities to slowly stir, regain colour and reanimate into a level of wakefulness. Beings who fully reanimate generally express disbelief, shock or agitation. Their movements and sounds may potentially trigger a chain reaction to stir nearby entities back into wakefulness; as such, any actions that would lead to reanimating a single instance is highly discouraged. Should the source of the disturbance be removed or suppressed, these beings are observed to slow down and revert back into suspended animation.

RPC-257-2 appears to be dimensionally in flux, and the positioning and contents of its side chambers always rearranges with each subsequent expedition. However, a trend can be observed that chambers housing smaller and more benign entities are always located closer towards RPC-257-1, while rooms housing larger and increasingly dangerous entities are located further away until the tunnel is obstructed at the very end. This method of sorting has been classified by four zones: Green, Yellow, Red and Black, with Black being the maximum distance that can be explored due to encountered obstructions (see below).

Discovery Log: Under the cover of night, an Authority recon team tasked with routine surveillance of the Hidden Sun Clan for any anomalous phenomena detected screams and sounds of combat within the dojo. As the team moved closer and discussed taking action, smoke from a fire began emerging from the windows as a visibly furious winged humanoid entity left the dojo at high speeds and flew into the cave adjacent to the dojo.

As the team contacted the Authority to send fire-fighting tools and materials to be airlifted to the afflicted dojo (due to its remote location far from basic infrastructure), a loud roar could be heard echoing from the cave accompanied with the repeated ringing sounds of metal being struck with metal. This went on for a minute, followed by a brief period of silence. The hostile entity then flew out of the cave and fled the scene at very high speeds (estimated 120+km/h) in the form of a large avian creature.


The dojo of the Hidden Sun Clan mid-destruction, as recorded by recon personnel.


Photographic analysis revealing the fleeing entity behind the clan's demise and the fire.

Due to delays in scrambling fire-fighting helicopters combined with the clan's remote location, the dojo was gutted beyond repair. Arson forensics indicates the fire to have begun within an archival room and supposedly spread with unusual rapidity, with most of the documents detailing the history behind RPC-257 as well as instructions relevant to maintaining various rituals related to RPC-257 having been destroyed in the fire.

It is believed that RPC-486 and Our Grandest Director RPC-316 successfully escaped during this commotion.

Incomplete log of RPC-257-2 entities

Foreword: Entities are labeled by their conventional names, to reduce any confusion caused by the repeated rearrangements of RPC-257-2's layout.

List of known escapees:
Designation Species Zone Notes
RPC-486 Kitsune Yellow RPC-886's biological sibling, resides outside Site-089.
RPC-494 Gashadokuro Red Released by RPC-486 by accident - see Incident Log 257-1. The only one of its kind. Successfully captured and presently contained at Site-089.
[REDACTED]9 RPC-316 Nurarihyon Yellow It is unknown when Our Grand Director this entity escaped RPC-257, and is believed to be directly referred to upon the wooden throne's engravings found in the empty chamber.

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