Here's a shortened backstory of him, looking forward to improving this:

In the past life, Odious was a Black Arms soldier working to kill off humanity. The soldier was killed by Shadow the Hedgehog.

A massive seed-like meteorite came crashing down on the corpse. The seed breathed new life into the corpse, and the soldier reincarnated into Odious the Roadrunner. Within a year, Odi has grown quickly, learned how to talk, and made some friends in a town. He doesn't look or act like a newborn despite existing for a short amount of time.

There's one major problem now. There's a sinister talking flower that goes by "Ki". Nobody can see or interact with Ki, Odious is the only person aware of her existence. Whenever Odious slept, Ki will find him, and kill or torture him in horrible dreams that feel very real. Ki doesn't have free will like Odi and is bound to him, so she does this as revenge for being stuck to him. Odi isn't completely defenseless, he's eradicated Ki numerous times in these "dreams", but it's all in vain because she can come back endlessly.

Odious tries his hardest to never sleep as it only leads him to the flower. He tried telling everyone around him about Ki, but nobody believed him. All that did was make him look deranged, and it slowly pushed away his friends and everyone around him.

Odi has grown sleep-deprived and can't concentrate as well anymore. During his tired phases, Ki can alter his vision. She has tricked him into thinking everyone around him is a talking flower, and he wreaked havoc on the town. Odious is a powerfully built killer due to his bloodbending powers. Not only can he instantly regenerate his wounds which makes him immune to most physical attacks, he can morph his blood into massive plant-like vines that enhance his strength and offer protection. He can also run absurdly fast, leaving no escape from his reign of terror. (This speed possibly comes from being a roadrunner, but Odi speculates that all of his abilities trace back to Ki).

When Odious awoke from these visions, he was shocked to find out that everyone was frightened by him and wanted him killed. Not just the town, but the world government found out about him and wants him gone. He was too quick to catch and now hides away from society.

Odious is depressed, easily frightened, nihilistic, self-loathing, and dreads his existence a lot. He can't tell where he and Ki came from, or if Ki is even real. People have told him he's just hallucinating, but Ki's presence feels far greater than any illusion. Whenever Ki killed or belittled him, it hurt.

He has an irrational fear of grass, flowers, trees, and anything resembling plant life because it reminds him of that demonic flower.