He likes to think that he can see all the details of her that makes her her.
He tries, of course. His years of quiet observation of his three best friends (with the occasional mischievous participation, of course, each rewarded with surprised looks and equally mischievous smirks) and sheer bookishness help. And he likes to think she lets him see. Either in the way they sort of purposefully-accidentally end up together in surveillance duties, or on the couch in the drawing room in front of dancing lights by the fire after order meetings at the pretense of doing something or the other. Except that those things almost always dissipate into nothing, and they both end up staying for far too long, neither one minding too much.
He watches as she steps out of her broom that day they escorted Harry out of Little Winging, how she lands with a grace honed from years of Quidditch practice, and swings one foot and then the other off her Comet Three-Sixty, with a nonchalance anyone would have dismissed as real. Except that he notices the tiniest of lines furrowing between her brows in concentration, and the tight lips anyone would've associated with the cold and Alastor's relentless paranoia. But he sees. He smiles at her as he opens the door quietly, and she smiles back.
The first time they spent the night together he tried his very best to memorize all the bits and pieces of her as she revealed them to him. With every touch and caress, he tried his utmost to study the contours of her - her delicate cheekbones, the soft underside of her breasts, the surprisingly sensitive inside of her knee. Up until he lost his mind in her, in them, he had tried to study the slight differences in her reactions, tried to experiment on what made her sigh happily or moan impatiently or catch her breath in anticipation. He still hasn't completely learned all her secrets in this field, but she assured him with every kiss and touch that she'd let him try again anytime. And he smiled as he realized he is most definitely the luckiest man on earth.
If he looks really closely he can make out a faint line on her upper arms where her school training jersey had ended and the sun's rampage had began heating her skin. He told her this once as he ghosted the very tips of his fingers on the supposed line while they snuggled on the couch. She shivered slightly (to which he inwardly smiled, an absurd sense of pride and pleasure coursing through him at making her shiver at his touch), then chided him and said he can't possibly see something from all those years ago. But still he smiled.
She had always said she wasn't the type to wear rings. And anyone else who laid eyes on her would've quietly agreed. Her notoriously pink hair, baggy jeans, and no-nonsense combat boots convince all of them. Except for him. When he quietly asks her to marry him - none of his other plans of grand gestures had worked out very well so far, and to be honest, he doubted whether Tonks would even want big gestures when all they really want was to be together - as they snuggled together on his slightly tiny bed. She shifts to face him from her too-comfortable nest on his shoulder and he knows the size of the bed was not a legitimate excuse to keep her as close as he does, but she presses her body to his anyway and her face breaks into the most beautifully heart-breaking smile he has ever seen as he brings out the tiny ring decorated by a single opal. He explains that it was his mother's, and could he possibly hope for the honor of placing it on her finger? She says yes, yes, yes, and sighs, saying she doesn't really like rings and laughing a bit. Later on he catches her looking at her newly-ringed hand appreciatively, and sighing, places a kiss on the tiny opal, a small smile playing on her lips. She never did take it off, and at this, Remus can not help but smile a ridiculously happy smile.
He likes to think that he can see all the details of her that makes her her.
He's certainly tried, of course. But in his heart he knows he can never fully learn every tiny thing about her. As she stirs beside him and arches her back in lethargy, her eyes fluttering and mouth opening in an almost imperceptible yawn, he smiles and thinks that that, of course, is no reason for him not to at least try. Her eyes open, finally, and in those big wonder-filled, slightly teasing black eyes that somehow sparkle with all her hope and trust in their future together, he knows there are a million tiny things about her yet to be found out, and he'd gladly spend the rest of his life trying.
Especially if he gets to see her smile like that.
