The Yin (in Japanese: 魄 Haku; Yin Energy) is a dark energy that is the collection of negative emotions and sins that people felt inside, and it plays a role in the 2002 videogame Shinobi.
Many centuries ago, the ancient demon blade, Akujiki, was forged. The blade is however, revealed to be inhabited by an age-old and demonic being that must consume Yin, the very darkness within every living creature in order to live and grow strong. As the demon consumes Yin, its power increases exponentially, and the souls inside will form into an amalgamation of spite and agony and sadness. Many have fought and died to acquire its power, for it is said that he who wields Akujiki can rule over the souls of men.
Hiruko Ubusuna was a skilled onmyouji (in Japanese: 陰陽師； sorcerer or medium) who lusted after Akujiki's power. After he was first defeated by the Oboro clan, he laid dormant inside the Kumano Shrine for decades before finally being set free. Upon his awakening, he sensed Akujiki's dormant power and devised a plan to awaken the blade. 4 years prior, the Oboro clansmen Hotsuma and Moritsune were locked in a fight to the death. The two brothers were the eldest members of the clan's main household, and they were forced to duel before the eyes of the high-ranking Oboro clansman Master Kuboshi and Moritsune's long-time lover Ageha for the clan's leadership role. This savage ritual was initially devised to suppress the demon blade's hunger by providing it a sacrifice that was filled with Yang, the positive light energy and spiritual opposite of Yin. The battle was swift, and Hotsuma prevailed as the victor. Despite his hesitance, Hotsuma did as he was instructed and killed his brother to end the ritual. Little did he know, this action initiated a series of events that would destroy his clan and bring such immense sorrow upon the world.
Soon after his awakening, Hiruko laid siege to the Oboro village, both as an act of revenge and to initiate his scheme to gain ultimate power. Unfortunately, the sword was nowhere to be found in the village, so he sent his Hellspawn army to search for it. Ultimately, he was informed that Hotsuma had it in his possession. He used his dark magic and Gojufu talismans to summon Hellspawn and reanimate the corpses of the slain Oboro and sent his legion of possessed Oboro soldiers to wreak havoc on the world. His ultimate plan, to kill Hotsuma and retrieve the sword, was underway.
In the end, Hotsuma rose to Hiruko's challenge and sought out his revenge. He cut down legions of Hellspawn and the corpses of his fallen comrades. He destroyed the Hellspawn weapon, Yatsurao, and finally slain Hiruko Ubusuna in the final battle atop the Golden Palace.
- In contrast to the English translation used in Shinobi, Haku is the Yin side of the spirit that remains in the body.
- Yin and Yang are both based on the ancient concept of duality known as Yin (darkness and negativity) and Yang (light and positivity).
- Haku is a component of Yin that remains in the body. When a being is killed by Akujiki, the blade sucks up their corporeal essence and their physical bodies vanish.
- When the player performs a tate (殺陣), the fallen enemies will release 3 times more Yin than when they are killed with a normal attack.