Amatsu-Mikaboshi, meaning the "August Star of Heaven" is the god of evil and of the stars, specifically the pole star in Japanese mythology. Despite being mentioned in Eastern lore, the exact details and characterizations of Amatsu-Mikaboshi are very cloudy or unclear, as he (or it) is rarely if ever mentioned in any of the typically referenced texts of East Asian Mythology.
From what can be gleaned and pieced together from ancient Japanese myths, Mikaboshi is not a physical god in the sense like Amaterasu or Susanoo, but a dark Force that existed before the universe, reigning alone in absolute darkness and control. This, however, proved to be untrue in a sense as Mikaboshi was in fact a fragment of the primordial chaos that existed before the universe and not being the chaos itself.
However, the Big Bang occurred which was the clashing of God and Chaos. After the defeat of the darkness, threads of itself scattered about and managed to slip by God and his angels undetected. One of these fragments came to be known as Amatsu-Mikaboshi. Mikaboshi attempted to regain the darkness but in one brief instance the iron control of the Dark Force, it was shattered by the movement of In and Yo, which brought forth the completion of the universe and the active chaos of life and movement, which later became the gods and humanity.
Even though solidity of the primordial darkness had been destroyed, its residue still lingered on in the hearts of all beings and is allegedly the cause of human passions. The idea of Amatsu-Mikaboshi as the god of evil is slightly a misnomer, however, as Mikaboshi is not a Japanese "Satan" or anything of the sort. It originated as an antithesis to the positive forces of life in Shinto, thus its lack of a singular form.
Amatsu-Mikaboshi is a force of absolute domination that feeds off of human emotions that, if left unchecked, result in social, emotional, or physical destruction. For instance, a desire for success can lead to greed and lust for power, which is the result of the influence of Mikaboshi's residue. Love for another can lead to obsession or jealousy, also result of its dark influences. In later centuries, certain creatures that are by nature dark or demonic were said to be connected to Mikaboshi in a sort of slave relationship to its power.
Souls that died with strong attachments and came back to hurt the living were said to have become physical agents to Amatsu-Mikaboshi's force in a more direct way than simple greed or lust when living, and such creatures as oni, Ama-no-Jaku, and demons were also results of certain natural elements falling prey to passions fed by Mikaboshi's temptations. The ultimate goal, it is said, was to absolutely destroy everything by dissolving it back into chaos, whereby the static, controlling power of Mikaboshi could return.