In Danganronpa v3, Kokichi acts sorta outgoing, mischievous, playful, lies a lot. Miu is...well, Miu. In the game, Kokichi and Miu aren't on the best of terms. But... ((spoiler warning, skip if you don't wanna be spoiled))
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Near the end of the game, it's revealed to the player that the characters auditioned for a place in the killing game. In the audition videos for Shuichi, Kaede, and Kaito, you see that their personalities are total opposites of what you see in the game. In that case, I imagine Kokichi would be shy, quiet, nervous/anxious and Miu would kinda the same way. Because of the personality switch, if Kokichi and Miu knew each other before the killing game I'd imagine that they would actually be good friends. :>