Misaki had been dating Misaka, Junko, Mitori and Dolly for about half a year and things worked out surprisingly well for the five of them. Everyone was accepting not only of each other's love, but also each other's love for the others in their arrangement. At some point, Kongou Mitsuko joined the arrangement; first out of interest for Misaka, but later adding another edge towards Misaki as well.

Calling back to the language of graph theory, by then there had already been one pinned to the fridge, reminding everyone about who was currently committed to whom. A simple visual solution to an otherwise complex problem, the difficult thing was not to draw the lines between the doodles, that represented each of them, but getting everyone to agree where the lines should be drawn. Misaki would know, she could read their minds after all. In the case of Kongou, it actually took more than a month, before she started being honest with herself, plus a week or two to get her to talk it out with Misaka.

"Aaaaand it's done." As far as Misaka was concerned, Misaki went back to her usual cheerful self rather quickly after her bag of remotes was returned, so it wasn't a big surprise, that she'd make a huge deal out of drawing a simple line. Truth be told, she was a little hurt in the beginning, feeling a bit like a stepping stone to the inner-most ranks of Misaki's clique 2.0, but seeing how Dolly and Mitori still had their relationship going on despite her being part of that as well, she was relieved in the end. "Guess I should start calling you Mitsuko from now on. I'll be in your care."
And then she snapped.

"SHOKUHOU!" The line between Kongou and Shokuhou had just been drawn, yet she immediately wanted to jump to given name basis, when no one, not even the author said or wrote "Mikoto" even once in the entirety of their relationship.
"E-ehm, M-Misaka-c-chan, is something wrong?" Shokuhou's shaking voice clearly expressed the fear she must have felt towards her as sparks of electricity were emitted in doses normally meant for Kuroko. The woman in front of her was not nearly as durable, let alone fit enough to dodge, so one strike would probably enough to end her. Even as her blood was boiling, Mikoto had to hold herself back, so as to not inadvertently cause more harm to her loved one than she wished to.

"Isn't it strange, that you still refer to her as Misaka?" Mitsuko was not quite sure, whether she should step between those two or not, given she was the cause of the fight they were having, but in situations like that, her courage had yet to fail her.
"Eh?" For someone, who could read minds, she sure was slow on the uptake. Was not being able to read the room part of her setting? Esper abilities usually did not come with weaknesses, however, much less such convenient ones.
"All I'm saying, is that you should perhaps be on given name basis with her as well, if that's what you're going to do with me."

Misaki dropped her pen and went silent. She left the room without uttering even a single additional word.
"What's with her?"
Mikoto let out a sigh. "It's that thing again."
"That thing?" Mitsuko was left with even more confusion than before. What was going on in their relationship? Shouldn't it all have been just fun and love?
"Mitsuko, did you ever wish for Misaki to call you by your given name?" What a weird question to ask. Of course she did! She loved her as much as everyone else did. "If so, she probably knows. But she won't know if I'm the one thinking that."

It was that again. The reason for all their disputes, even before they became a couple. Misaki couldn't read Mikoto's mind – of course not – so she never knew, that she wanted to be on given name basis with her. Even if she was called Misaki by her all the time and she was on given name basis with everyone else, she still called her Misaka-chan, because that was the way, that felt natural to her. How stupid could she be?

"You see, even if I were to willfully discard all my guards, Misaki still won't use her powers on me. I bet it's because the last time someone invited her into their mind was very traumatizing." At least, that's what Mikoto wanted to believe. She couldn't ignore the thought, that she herself might be at fault for how she felt as well, though. After all, whenever Misaki had been criticized for her usage of the power, it was always by her.
"What do you suggest we do then?" Mitsuko asked.
"Let's leave her to Mitori for today. I'm sure it'll take a nurse to cure her." Mitsuko remained silent, but her face told Mikoto, that she didn't believe her. "What's wrong?"
"Mitori is not actually a nurse, is she?"

Author's Note

So yeah, I just realized, that Misaka was actually Misaka's surname, meaning that Misaka Misaki could be Misaki's name if they married. I don't know, how I could ignore that for so long.
Also half a year totally checks out for everything I wrote here, given that the Mental Out Arc takes place just three months after the Daihaseisai, not to mention the other time skips I had. Surprise canon!