This is kind of interesting. A new Famitsu ad describes the Master Sword as "corrupted". This was fairly obvious from what we've seen so far, but the ad shines a brighter light on it:
Neat Zelda add from the new Famitsu.— Game Data Library (@GameDataLibrary) February 18, 2023
The right text reads "The master sword, corrupted"
The small at the left says (shortened) "In the new title its appearance will undergo a major transformation" pic.twitter.com/jiVubwSPSJ