Do not use all caps for emphasis; use italics.
Midday is not hyphenated.
Do not capitalize the first word of a dialogue tag that follows the dialogue.
The midday sun flashed off his blade as it swung viciously through the air. “Traitor!” he screamed.
Still not quite right… I can see what the writer of the original was trying to say, but this isn’t it. The way the sentence is written, it implies that the sword is vicious, not the person wielding it. A small change seems necessary: The midday sun flashed off his blade as he swung it viciously through the air.