Tales of unknown Origins

Some call them demons, ogres or even giants in truth it doesn't really matter what they are called because it's not the name what makes them terrifying, but the tales of their unmatched strength and ferocity, they are often described as unstoppable or unbreakable, the primal fear they cause is what is ingrained in peoples minds and souls.

"Oni of Infinite Rage."

Onis are known for their strength and will that they use to fuel their anger and rage. Some say that to defeat an Oni, you must cut off all of its limbs before it reaches the ground again. Otherwise, it will become whole again and resume its attack. In some regions, Onis are worshiped as ancestors of their village. When a villager dies, they may be cremated and brought to a mountain where they can become an Oni. They would then be called back as family members and protect their village from harm. Since Onis are said to be demons that protect their villages, they are treated like royalty in some regions.

Oni Traits

Your Oni character has the following racial traits.
Ability Score Increase. When determining your character’s ability scores, increase one score by 2 and increase a different score by 1, or increase three different scores by 1.
Creature Type. You are a Humanoid. You are also considered a Giant for any prerequisite or effect that requires you to be a Giant.
Size. Onis between between 7 and 8 feet tall and weigh between 280 and 340 pounds. Your size is Medium.
Speed. Your base walking speed is 30 feet.
Darkvision. You can see in dim light within 60 feet of you as if it were bright light and in darkness as if it were dim light. You discern colors in that darkness only as shades of gray.
Powerful Build.  You count as one size larger when determining your carrying capacity and the weight you can push, drag, or lift.
Languages. You can speak, read, and write Common and Abyssal.
Duality of Body and Soul. As an action, you can switch between your true form and a specific humanoid form that is linked to you from birth. This form is either human or another race your DM deems appropriate for your background or the setting. This form can be of different height between Medium and Small, weight and complexion.

Blue Oni

Ghost-like creatures born from storm and lightning.
Storm's Born. You have resistance to lightning damage.
Phantom Steps. As a bonus action, you can jump up to 30 feet, without provoking opportunity attacks. You can use this trait only if your speed is greater than 0. Immediately after you use your Phantom Step, each creature within 5 feet of you takes 1d8 lightning damage.

This damage increases by 1d10 when you reach 5th level (2d8), 11th level (3d8), and 17th level (4d8).

You can use it a number of times equal to your proficiency bonus, and you regain all expended uses when you finish a long rest.

Green oni

Voracious demons of gluttony and Pestilence.
Unnatural Resilience. You have advantage on saving throws against poison, and resistance against poison damage.
Demonic Bloodline. Your resilience in battle is unmatched. As a bonus action you can push your body to close your wounds, for the next two turns you regain hit points equal to your proficiency bonus. You don't gain this benefit if you have 0 hit points.

You can Regenerate a number of times equal to your proficiency bonus, and you regain all expended uses when you finish a long rest.

Red Oni

Forged by fire and blood, unstoppable creatures of wrath.
Hellish Resistance. You have resistance to fire damage.
Wrath of Asura. As a bonus action, you can awake the power of your blood. This awakening lasts for 1 minute, until you die, or until you end it as a bonus action. When you awake, you add your proficiency bonus to your damage with melee attacks. You can awake a number of times equal to your proficiency bonus, and you regain all expended uses when you finish a long rest.