From AO3. A repost of a story from late 2017.

The pen scratched across the paper, etching words in extravagant detail. Sorin had strained to recall every moment of it. From when he was woken up that morning by Ellen, bubbling with excitement – to his daughter making her first breakthroughs – to dinner, which had been so fun that he didn't focus on remembering it as much as he should have.

When he settled down at the desk in his and Ellen's shared bedroom, the dark wood seemed to coax those memories back to the surface. The day's event fell out of his mind and onto the paper, transferred into the fourth journal of his life. The other three sat on a bookshelf above the desk, all in different states of wear and tear over the years.

As he recorded the last dredges of the day, a small noise distracted his hand. Turning to look, Sorin briefly took in the picturesque image of a red crib with peach sheets inside. Nestled in the bundle was a small baby, quietly sleeping. They had not stirred, so Sorin glanced back at his wife. She too, was fast asleep, but had turned over beneath the quilt and covers. With a silent promise to join her soon, he completed the last affairs of the day, then turned to read back over everything. He took in each memory and word in turn, comparing it to what he recalled. He smiled as he noticed a sentence, circled and marked in pen.

She learned to crawl today! Happy memories floated to the surface upon reading those words. Their daughter was growing up fast, and today had been a surprising development. She began to move around that afternoon, crawling out of the living room and into Sorin's office space. Feeling something bump against his leg, he had looked down and seen his daughter, smiling up at him. He and Ellen nearly cried with joy at the sight. His wife was quick with a camera, taking photos and saving them onto the computer – but not before she and Sorin encouraged their daughter to crawl around more. Ellen had him take a break from designing and sit on the floor, letting the baby move to him again, before going to get the baby journal they were keeping.

Like Sorin's own necessary habit, Ellen kept religious logs on the baby's progress. She said that it would be good if Sorin ever wanted to look back on "things related to his daughter", instead of trying to find them mixed in with meeting summaries and client information. He was grateful for it, especially since Ellen had taken to including pictures, too.

With a happy sigh, he glanced once again at the sleeping form in the crib, the memories ceasing their playback. He read on through the next section. It talked about a couple conferences that day, a few plans for the newest invention, a conference call with his retired father… and dinner.

Sorin couldn't help another grin as he read back on his words. It started with Ellen sitting their daughter in her high chair and teaching Sorin how to use a potato peeler – according to her, for the tenth time – while their daughter looked on. With wide eyes, she observed Sorin using the unfamiliar tool and Ellen cutting up vegetables and chunks of meat. He took note of this behavior and started to hold out the potatoes to her, jokingly asking for her approval. Of the six, she accepted five. However, the last one was taken out of Sorin's hands and tossed onto the floor. It mashed against the tile with a splat!, and Sorin stared at the result with a horrified expression.

"Oh, no!" Ellen's bell-like laughter rang out behind him, and Sorin felt heat rise to cheeks from the embarrassment.

"I'm so sorry," he said softly, but Ellen only waved it off, trying to bite back the rest of her amusement.

"We just won't use that one! Here, let me get it." Seizing a few paper towels, she and Sorin cleaned it up together, throwing the contents away. "Do you want to cook the vegetables, now?"

"I can." He nodded to her and went to the oven, carefully scanning the recipe. It seemed easy enough. He followed the instructions to the letter, save for Ellen's penciled-in changes. Written in her tidy hand, he took those notes to heart more than the printed text. She was always right.

Tonight was wonderful. This entire day, beginning to end, was filled with happy memories. Sorin didn't want to forget a single one. His weary eyes, blurry with exhaustion, reached the end of his diary. He set down his pencil and turned to face his daughter one last time. Sorin's eyes slowly slid towards the golden plate screwed on the side of the crib, reading the words silently: Sonia Selena Sprocket.

Her name was spelled in a tidy, engraved script. He reached out to run a thumb over the middle name. For a moment, he remembered his sister, remembered that fatal night that he relieved in some passing nightmares—

He only hoped that she was happy for them. And that she was willing to be Sonia's guardian angel, as Sorin had taken to calling her. Was she watching all of her progress, too? Did she remember all the things that Sonia had done so far? Sorin stared down into the crib with a sadness in his eyes.

I don't want to leave you behind just yet, Sonia.

Each morning he would have to wake up and relearn his entire married life. Sorin knew that he and Ellen were married, and then remember they were blessed with a child. The former had been sticking with his mind as of late – but the latter…

He stayed and watched. The seconds trickled away like sands in an hourglass, filling up the room with a strange sense of melancholy. He strained his mind, trying to etch this moment into his brain. He wanted to remember so much – everything – about today. So much had happened that he refused to forget.

He knew that the process was ultimately futile. However, it did not stop Sorin's hands from tightening, pressing against each other as he closed his eyes, holding back tears.

Just this once. Just this once, I want to remember you, Sonia. Just this once, please. Let me remember this.

Ending his exercise, he gave a one last longing look towards his daughter. She made a sound in sleep, happy and restful. When she did not wake up, Sorin turned back to his still-open journal, marking just a few more words on the day's pages.

"I watched her sleep. I will miss her dearly when I, too, sleep. Sonia, I want to remember you today. Please. Let me. I love you with all my heart."

With that, he closed the journal behind him, clicking off the dim light. Standing from the desk, Sorin stretched, crawling into bed soon after. Ellen, her eyes still closed, turned over, falling into his welcoming warmth. Arms about his wife, he placed his head against the pillow and succumbed to sleep.