Kami and Megami

The Kami, (Japanese for God), and Megami, (Japanese for Godess), are godlike spiritual beings that preceded the Shinigami, and are by some believed to be their ancestors. They were the ones who originally created the Soul Society, The World Of The Living, Hueco Mundo, The Valley Of Screams, Hell, Heaven, Spirit Dimension, and the Realm Of The Gods, so they are seen by many as literally being Gods, although nobody knows for sure. In fact, most people believe they're actually myths and not even real to begin with.

Overview
The earliest known history of these strange beings, (to people who  believe in them at all, that is), dates back to before the founding of the Gotei 13, or even sustaining order in the Soul Society. All of the eight dimensions were in a constent state of war and chaos, until the Megami's and Kami's came along to quell the chaos and create peace. Although they did not have Zanpakuto or Kido, because they weren't invented yet, they were able to do so with their intense and monstrous spiritual energy, speed, and physical strength. Shortly after they disappeared they went on to create the Realm Of The Gods, and disappeared within it forever, never to return to the Soul Society.

Physical Traits
Although much of their appearance is a mystery, Shigakuni Genryusai Yamamoto, who was but a small boy at that time, remembers vividly exactly what they looked like. Their true appearance was concealed, but he remembers that all the males, (the Kami's), wore large, thick, blue robes with red stripes going through them, while the females, (the Megami's), wore large, thick, red robes, with blue stripes going through them. That is except for the three most powerful, who wore large, thick, pure black robes. These robes even concealed their faces. Each one of them were massively muscular, and were frightening to look at.

Godlike Spiritual Energy
This was their most identifying trait, a spiritual energy that, according to Yamamoto, even to this very day, would make him tremble in absolute fear and terror.

Godlike Speed
Another reason they were so feared, they were able to traverse the entire universe in a matter of seconds with this speed.

Godlike Strength
Any opponent that they faced, if they were strong enough to get past their spiritual energy, could be killed and destroyed with just one punch. They could even combine their speed with their strength, for even stronger punches.

Shinjinbukaikai
Japanese for Godly Release. Atlhough they didn't have a true Zanpakuto, they did have the first Katana which served as the inspiration for Nimaiya Oetsu's Zanpakuto. They just had one power release, which was known as Shinjinbukaikai, which allowed them to release all of their spiritual energy at once. They had several different fighting styles once this happened. There was also no inner spirit to these katanas like there are for Zanpakuto.

Heijou Rantou, Shinjinbukaikai
Japanese for Normal Fighting, Godly Release. Once this was released, they could just continue fighting normally if they so choosed.

Zangeki, Shinjinbukaikai
Japanese for Slash, Godly Release. This was an ability that allowed them to slash with their katana, using all their power in their katana in one attack.

Aoriwokuu, Shinjinbukaikai
Japanese for Blast, Godly Release. This ability allowed them to fire one giant blast of energy, (which was later one of the two inspirations for the creation of Kido), which contained all of their spiritual energy.

Tahatsusei Aoriwokuus, Shinjinbukaikai
Japanese for Multiple Blasts, Godly Release. This ability allowed them to fire many giant blasts of energy, (which was later one of the two inspirations for the creation of Kido), which contains large amounts of, but not all of, their spiritual energy each.

Reiatsu Butsubutsu, Shinjinbukaikai
Japanese for Spiritual Energy Eruption, Godly Release. This abiity allowed them to cause their enemies to erupt into flames using just their spiritual energy's intenseness alone.

Standard Equipment
All that is known about their equipment is the cloaks that they all traditionally had on, as mentioned above, as well as their regular katanas, known as the predecessors of the Zanpakuto.