Black Dragon

The Black Dragon (黒竜, pinyin: Hēilóng, romanji: Kokuryuu) is one of the four dragons who serve Shangdi. Other names for the same dragon include Lílóng (驪竜) or Xuánlóng (玄竜). Unlike many East Asian dragons, the Black Dragon is depicted as a spiteful and evil entity. Weak to light, it lurks within areas of darkness. The god is often tied to the night or the sea floor. Depending on the source, it views the White Dragon as its nemesis.

Within the Five Elements philosophy, it is a holy deity who represents the north and is analogous to the Black Tortoise. Taoism has it act as the Black Dragon God for the Northern Sea, Ao Ming. He dwells in the oceans and the darkest depths of rivers.

The Harukanaru Toki no Naka de series has its own take on the Black Dragon for its parallel universe.

Harukanaru Toki no Naka de
Since the dawn of time, there has been two dragon gods in the parallel world: the White Dragon and the Black Dragon. When their powers are united in harmony, they are known as Yinglong. The Black Dragon represents yin: ending, rest and death. It can unleash heavy clouds of defilements, causing man and beast to become mad by its influence. The god often forms bonds with any soul in the afterlife. When it descends into the human world, black butterflies may appear to signal the god's arrival. These butterflies represent departed spirits and are tinged with various spiritual defilements.

A master of darkness and other malevolent energies, the Black Dragon has little need for sacred servants. Two Black Kirins guard it and exist to be the opposites of the White Kirin. These Kirins can manipulate darkness to their will, being second only to the dragon god. Should these Kirins be somehow defeated, however, they will obediently serve whoever bested them in combat.

Like its opposing dragon god, the Black Dragon watches over humanity within its own heavenly realm. If they become too close to humanity and their emotions, they risk losing their own godhood and becoming human. The dragon gods have been predominately depicted as male, but female versions are known to exist.

If a young maiden is chosen by this god to be its priestess, they gain a fraction of the Black Dragon's powers. She gains the power to summon and calm vengeful spirits, can absorb impurities into herself, and may even have the power to completely stop time. She can assist a White Dragon Priestess with sealing vengeful spirits, though she doesn't possess the ability herself. Due to her abilities, she isn't weak to defilements like her counterpart and is resilient to curses. If she feels it is needed, the priestess can sacrifice herself to summon her dragon god or may alternatively let her dragon be summoned by the White Dragon Priestess.

Earlier eras failed to recognize her as a priestess due to the prominent belief that there was only one dragon god. She was informally called "the other Dragon God Priestess" (もう一人の龍神の神子, mou hitori no Ryuujin no Miko) as a result. By the later Heian period, the Black Dragon became common knowledge for those who studied the parallel world's history. A priestess who is linked to the dragon god is called the Black Dragon Priestess (黒竜の神子, Kokuryuu no Miko). The dragon god can use telepathy to speak to its priestess, either by ringing a bell (as a warning) or directly with human words (if the situation is urgent).

Ancient Times
When humanity matured long ago, they began to worship the dragon gods and the four sacred beasts. Humans granted them names and revered them. The Black Dragon was content to watch their progress until they began to outnumber the residing gods throughout Nakatsu Kuni. Not all of the entities within the realm were worshiped, the Black Dragon thinking that humanity had rudely ignored their status to be ruled by them. Enraged, he separated from the White Dragon and began to terrorize the mortal realm. He thought humanity unfit to protect and sought their immediate destruction. People feared him and called him names such as the "Bloodied Serpent" or "Yamata no Orochi". They never suspected that the beast was a dragon god who had previously nurtured them.

Unable to completely descend into the mortal realm, the Black Dragon demanded that a worthy sacrifice be fed to him. He desired a young girl with exceptional spiritual powers so he could unleash his true powers into the human world. The maiden desired to protect her home and bravely opposed the Black Dragon in a tiring war. During the climatic battle, she used every ounce of her strength to summon the White Dragon. Foiled by the burst of his counterpart's yang energy, the Black Dragon was quickly subdued. Put into a deep slumber, he waited for his comeuppance within the faraway land, Tokoyo no Kuni.

About 360 years later (six years before Harukanaru Toki no Naka de 4's main story), the Black Dragon had regained its strength and tried to revive himself. A Nakatsu-Kuni princess sensed him coming and, knowing that it only sought destruction, tried to prevent his reemergence. She and her two comrades fought the dragon god, but she was only successful in partially sealing him. Encased in a circular prison, his grudge against humanity manifested as unrelenting heat, scorching the plentiful lands of Tokoyo no Kuni to become arid wastelands. He earned the distasteful name as the "black sun god", Magatsuhinokami (禍日神).

The Black Dragon continued to hunt for a proper human sacrifice, momentarily hosting himself within the king of Tokoyo-no-Kuni. He sensed a priestess designated to his counterpart and sought to absorb her into him. History repeated itself, as he was denied once more. When his twin awakens, the Black Dragon gladly follows its will to destroy. Begrudgingly impressed by humanity's power, he soothes his grievances and retires to the heavenly realm.

Later Centuries
Choosing to follow the decision of his brighter half, the dragon god does not directly interfere with human affairs. Both dragon gods now believe that only humans can create their own happiness and future. It will only act if the residents have a fervid wish and pray for it to save them. Should the parallel world experience peril, it may choose a maiden within the world or summon her from another world to restore peace. Despite their general passiveness for humans, each dragon god cares dearly for their respective priestess. The Black Dragon will try to protect her from harm and may even sacrifice itself to save her.

If the dragon gods are weakened, a new dragon god can be reborn into a human-like form. This is possible so long as a dragon god's throat scale (逆鱗, pinyin: nìlín, romanji: gekirin) remains. The scale represents the dragon's power and spirit, its true self. If a dragon god removes it or if it shatters, their current form will cease to exist. When the Black Dragon's scale glows or resonates, the person holding it can use it to enhance any yin dominant magic, such as spreading curses or defilements. It can also be abused to fuel an endless supply of vengeful spirits.

During the Warring States period, a powerful sorcerer known as Nankoubou cast a powerful curse on its other half. This weakened both dragon gods severely and caused the Black Dragon to call for its priestess in the modern world. Its priestess –who feared and reviled its presence– refused to accept or acknowledge its blessings throughout her life. With its white half disabled, the Black Dragon lacked the power to summon her directly.

A new Black Dragon arises with the White Dragon's resurrection. At its priestess's behest, the dragon deity uses its powers to stop the destruction of the modern and parallel worlds. Like its counterpart, the deity is too weak to use its full power. It can only stall the worlds' collapse to a crawl. It resumes its duties in the parallel world once the flow of the Five Elements is corrected.