Alright you kept it nice and short. I do wanna make some fixes to that first sentence tho:
Shiro is a martial artist with a big heart and a friend who was corrupted by power. He'll do whatever it takes to show him the light, but can you change someone who doesn't want to change?
Since it's a one-shot comic, there's not many details to it that need to be covered in the blurb, so I guess this is good for now.
Looking at your other blurbs, you seem to have this recurring thing where you totally understand the idea of keeping it short but you still have a lot of adjectives that can make it a bit hard to understand. People move fast on the internet, so you gotta catch up with them:
Timmy's Angel
Timmy is a shy kid forced to endure bullying. Little does he know an angel is looking out for him.
Celestial Terrestrial
Caleb Connors is dragged into the fight of his life when a man with unholy powers tries to kill his guardian angel. Can the unlikely duo find the strength to defeat him?
(for this one, I just think "the fight of his life" would be better than "a fight for his life" since it's a more common phrase and more intense sounding)
Xenoscape
When Tara finds herself stranded in a mind-bending alien realm, she must conquer its dangers to survive. But can surviving ever be a replacement for being happy?
Larger Than Death
When a mysterious man descends into Hell in search of immortality, he invokes the wrath of its King. Will he reach eternal life or be killed on the spot? Only his true identity holds the answer.
You don't really need to explain the personalities of the characters unless it's like a super important thing to the plot (for example, I didn't think it was that important to know that Shiro from Goodbye, Rival is energetic). Your readers will understand their personalities when they read the story.