Summary: The first time was Ron's fault.
For pezzae, who requested 3 times Hermione and Ginny bonded over Ron being an idiot. I'm sorry, Jess, I tried, but for some reason writing Hermione and Ginny together was ferociously difficult. In the end I turned the prompt inside out and made the whole thing into crack. I'm still not sure how successful it was.
During her early years at Hogwarts, Ginny's attitude towards Ron's other best friend could basically be summarised as "Hermione who?" She didn't mean to be blinkered, but she was teetering under the weight of the world's hugest and most awkward crush on a boy who basically looked at her, when he looked at her at all, as though she was a bizarre and occasionally embarrassing bug from another planet.
Except, maybe, for that one time he saved her life, but she'd been unconscious for most of that, so she didn't get to enjoy it. Anyway, probably he ignored her the whole time.
The point was, if Ron hadn't messed up a simple binding hex during a DA practice in Ginny's fourth year, she would never have voluntarily spent eighteen hours at Hermione's side, the two of them shadowing one another's steps and trying to keep from their teachers the fact that their wrists were magically bound together, while they worked out the counter-spell, and she would never have learned that if you got Hermione tired enough, she could go into giggle fits that lasted past the point where she could no longer breathe.
Also, she knew a completely different set of breakfast cereal jingles to Ginny.
The second time was Ron's fault too. Sometimes, Hermione pointed out acerbically, things that had been tucked into corners in the Room of Hidden Things should stay there. They definitely shouldn't be taken out and left lying about the Gryffindor common room where innocent friends and sisters could pick them up.
"Please don't panic, girls," Madam Pomfrey said wearily. "Accidental telepathic bonds are very common; we see them every year. Just get a good night's sleep and I expect it will have dissipated by morning."
She didn't say anything about the dreams. To Ginny's relief, the next morning, neither did Hermione. She did avoid Ginny's eyes for a while, though.
Actually, all the times were Ron's fault. Trainee aurors were specifically told to remove significant items like engagement rings before they entered the practise space, if they were working on higher-level influence or emotion hexes. If first year trainees like Ginny were told that, second years definitely ought to know.
It was the first time since she'd started at the Academy that Ginny's year had gone into a joint training session with the second years, so it was the first time she'd come up against Ron or Harry. Harry grinned at her from across the room, the flash of smile enough to distract her so that she was caught full in the face with somebody's hex, right as she managed to grab Ron's hand in a completely standard immobilising grip. The engagement ring on Ron's finger burned hot against her palm, making her hiss and let go.
A moment later she'd almost forgotten the incident, whirling to spar with somebody else.
The first she knew what had happened was a rush of heat and want and tingling awareness that swept through her as she slept that night, making her sit bolt upright.
"Oh no," she whispered.
Oh god, Hermione thought in her head.
Not this again, Ginny thought back. Is it this again?
It's not ... Hermione gasped and broke off, finishing the thought with what felt to Ginny like difficulty. It's not just telepathy, this time. I can feel ...
Ginny could almost see her, eyes wide in the darkness, mouth slightly open, the bare skin of her shoulders pale in the ...
"Bad thoughts," Ginny muttered desperately. "Bad, bad inappropriate thoughts about my brother's fiance."
I'm not thinking them, Hermione agreed. Ginny had an impression of gritted teeth and hands clenched in bedclothes.
Definitely not, Ginny thought. I don't even like you like that. I like dark-haired girls.
There was a moment's deliberate silence.
Boys! Ginny thought. Dark-haired boys, I meant. Harry, I like Harry! She could feel Hermione giggling, desperate and overwhelmed.
Ginny was definitely going to kill Ron in the morning.
She just had to survive the night first.