Square Enix recently explained the significance of wings adorning characters like Sephiroth in Crisis Core FFVII and FFVII Remake. The explanation delves into the symbolic meanings behind the wings of Sephiroth, Genesis, and Angeal. It's important to note that the discussion contains spoilers for the storylines of both Crisis Core FFVII and the original Final Fantasy VII.
Angeal and Sephiroth's wings are on the same side due to their deep connection with the Buster Sword. Angeal, the initial owner of the sword, passed it down to Zack, who later handed it on to Cloud, Sephiroth's adversary.
In contrast, Genesis' wing is positioned on the opposite side of Sephiroth's, reflecting their distinct origins (created by Project G and Project S). While Angeal's white wing serves as a symbol of choosing the right path, Sephiroth and Genesis' wings convey the opposite message.
The explanatory post, shared on October 4, 2023, carries an additional layer of meaning, as the date can be read as "tenshi" (angel) day in Japanese. For a detailed look at Square Enix's original post: