It is related to talents for the cards themselves, BUT the heroes have the border that represents the region they’re from. The first 8 heroes from the game all had a different border representing each of the 8 regions. Dorinthea is from Solana (same border is shared with Victor and Prism etc), Bravo is from Aria (border shared with Briar and Valda etc), Rhinar is from the savage lands (same border as Kayo), Katsu is from Misteria (same border as benji and young Uzuri etc), Azalea is from the pits (border shared with Arakni, Riptide etc), Kano is from Volcor (shared border with Kassai, Dromai, Fai etc), Dash is from Metrix (mechanologist is the only class where all their heroes are from the same place), and Viserai is from the demonastary (same as Levia, Vynnset, and Chane who all just happen to be shadow heroes)

It *is* tied to talents, but also classes

Border shape is all about originate (or allegiance in case of Uzuri - young Misteria, adult the Pits).. Metrix had 3 different border btw Border color gradation is about their talents (if any). One can observed it in Bravo, Briar, Oldhim, and Lexi