the character designs of XII (and in turn, XIII) are actually based off of the character designs of when they first Debuted. for the most part at least (lol Clark and Ralf)
Athena and Kensou debuted in an arcade sidescroller called "Psycho Soldiers"
and there you go, thats where the hair comes from
Kensou looked different himself before XII(I)
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http://img.imgcake.com/LtM/1202942476287.jpg