Nice things make him angry and her wary. In his life nice things are false, for personal betterment rather than aiding others. In her life nice things are lies hiding terrible truths that make it hurt all the more. They aren't a pair for nice things. So his teasing words have never been a problem and her violence with books has never been a deal breaker. Soul and Maka make it work without nice things and they like it that way.
Maka always thinks of her Papa as a nice man. He has always been nice to women, too nice. That's the problem. He has also always been nice to her. That makes it hurt all the more. His actions are appalling, disgusting and she won't stand for it. But it's so much harder to be angry when he looks and speaks to her like that. It makes the deception sting and his over exuberant but not at all sincere apologies burn. Not Soul though. Soul is nothing if not upfront. His reactions to Blair's advances are an embarrassment to them all, but at least he doesn't deny them. Even though he's her weapon and her partner and should have more respect for women, for her, she can't stay mad at him. At least when he tries to talk her down from a rage he isn't nice about it. He's just Soul.
There is no denying that Soul comes from a nice family, one known for their skill and social aptitude. His whole childhood he is haunted by his nice brother with his exceptional musical skill. His whole childhood he haunts his family with his exceptional attitude and not nice music. When people recognise his family name they always want to know; why be a weapon, what happened? They always ask cautiously, carefully, considerate. It's none of their business. It's none of her business either, but at least when she really wants to know, she demands instead of dicking around. But that's just Maka.
They've never been nice, but they've always been loyal. He thinks there's a difference between the two and he's happy to leave it there. He doesn't think twice about throwing himself over or in front of her. Whether they face Shibusen's greatest meister or an unknown adversary with black blood he does not waver. Since shaking her hand that day by the piano he has known he will die for her. That's what cool weapons vow to do. He's not being nice. He's doing his job.
When he wakes up screaming she doesn't think twice about taking his hand. He's her scythe, her partner, hand holding is just something they do. She's relieved he's alive. It gives her more time to surrender herself to guilt. He won't let her though, not for long and she channels it into other things. There is nothing nice about running him a bath or re-dressing his healing wound. It's something that needs doing and so she does it. Any good meister would. After all, a meister is useless without their weapon.
The Black Room is scary and dark and wallpapered with insanity. It's harsh and dangerous and screams do not enter. But when he thinks about it, so does he. At first it surprises him when she arrives dressed in black, but angelic soul aside, it's not like it doesn't suit her too. She stomps on his foot when they dance, but the faith in her eyes fixes the pain. She knows he will pull her back. The feeling sliding through his soul isn't nice. At least, he tells himself it's not.
She wonders when she started taking his hand for reasons other than needing him to transform. She decides it was probably around the same time they realised that resonating increased her soul perception and other abilities. When her fingers find his on the couch she tells herself she's training her soul perception because the movie is boring. The feeling of his thumb rubbing across her wrist is warm, but it's not nice. Or so she says.
When he says those five words it almost sounds like he's saying they need to add milk to the grocery list. There's nothing nice about it, just normal. She has known it since they started of course, but it surprises her how much she likes hearing it out loud. Of course, she already knows, but when facing down another battle to the death it's kind of cool to hear it. Besides, none of the other weapons have made such declarations to their meisters. It's not just a promise, but a fact. He will follow her wherever she goes. Nice doesn't factor into it.
He knows he's felt it longer than her and he knows that she's scared so it surprises him when eventually it is her that makes the first move. Her hand is warm in his like it always is and her lips are light against his mouth. She backs away fast, but he holds her tight. There's a feeling spreading out from his soul that moves like the insanity of the black blood but is the exact opposite in meaning. When he kisses her again and she lets him, he recognises the feeling. He murmurs resonance and it is nothing nice at all because it is so much better.