Jay Ukyou
Resistance is Futile
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Men generally don't apply '-kun' to someone older than them, but especially not for a girl older than them, so Haru defaults to '-san'. If he was a more vulgar guy, he could call a girl older than him '-chan' and it gives off an air of hitting on them. Or if he was trying to be very familiar/casual or show he doesn't care/respect her, he wouldn't use an honorific suffix at all. (Sort of like how Rei would speak. In fact, I think Rei just calls everyone by their last names or 'you'.)
Jou uses 'kun' with the girls because they are all younger than him. Using 'san' would be too formal. Using 'chan' is okay, but it sounds 'cuter' and sort of like he has a crush on them if he used it with Mimi or Sora (or Hikari, Miyako or Meiko when they're all teenagers, but when they're MUCH younger, he could just use 'chan' for everyone, including the youngest boys like Takeru and Iori if he wanted).
Jou uses 'kun' with the girls because they are all younger than him. Using 'san' would be too formal. Using 'chan' is okay, but it sounds 'cuter' and sort of like he has a crush on them if he used it with Mimi or Sora (or Hikari, Miyako or Meiko when they're all teenagers, but when they're MUCH younger, he could just use 'chan' for everyone, including the youngest boys like Takeru and Iori if he wanted).