I'd always just assumed Kanji beached his hair, that's why when I saw him in the epilogue I was just like "Oh cool, he let his natural hair color grow back out." (though if it really was only like 3 months between Arena and Golden Ending, I dunno how his hair grew in that quickly)
Naoto is the one that confuses me. She's got blue hair, but unlike characters like Eikichi or Ulala, it's not really in character for her to dye it.
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