The Oni sub-species

The Oni sub-species was originally classified as a genetic mutation in the Giant species. These creatures originally came around after male Humans would mate with female Giants, the male humans generally not surviving the encounter. Over time, the descendants of these couplings became shorter and shorter, but they retained the strength of their Giant heritage. However, this proved to be a problem for them, as they realized that they, quite literally, couldn’t live normal lives as just about everything they touched would be destroyed, unless it was made by Giant standards.

After several generations of this mutation, a new mutation sprung about, as several of the newborns were found to have small nubs on their heads. When these newborns grew to be adults, these nubs grew to be horns. The horns seemed to act as limiters, allowing the much stronger beings to interact with the world at large. Humans grew to call these beings “Oni”, so this was the name that they took. An adult Oni stands at approximately 14-18 feet tall, with their horn(s) adding, at max, another foot.

Onis have the unique ability to break off their horn(s), and in doing so they regain their natural strength afforded to them by the Giant heritage. However, this comes with a heavy price. Upon breaking their horn(s), an Oni loses any and all spiritual abilities, including the ability to communicate with their Zanpakuto spirit should they be a Shinigami.