The flickering effect you're seeing is due to the thinness of the blade in certain angles—at specific frames, the pixels can momentarily disappear, creating a blinking illusion. This is a common visual quirk in pixel art when dealing with very narrow elements.
If the effect doesn’t suit your style or feels distracting, you have a couple of options:
- Swap the off-hand item for something with a thicker silhouette
- Manually adjust the sprites by adding a few pixels to the blade in an image editing program to ensure it stays visible across all frames