I'd suggest looking on websites like MangaFox or MangaReader. They often have a wide range of manhwa, including 'A Returner's Magic Should Be Special'. But be aware that the legality of some of these sites can be questionable.
The magic of a returner in the manhwa and anime is very special. It usually comes with hidden powers and unique traits that drive the plot forward and make the character stand out. Also, it might have some rules and limitations that add to the complexity and excitement.
The specialness of a returner's magic lies in its rarity and the way it gives the character an edge in various situations. It might have unexpected effects or be tied to a profound backstory.
The magic could be special because of unique powers or abilities that the returner acquires. Maybe it has rare effects or can be used in unconventional ways.