He will never forget this moment.
Never, may he live a thousand years: the wintery light as it peaks through the casement, warming the ivory nursery; the voluminous folds of white-lace curtains that ruffle behind him, cushioning his trembling back; the feel of the chaise longue beneath him, its cobalt fabric as soft as its decorative buttons are hard. Despite his most recent growth-spurt, his feet still dangle off of the davenport's gilded edge, but for once he hardly notices—there are other things, today, more important things, to make him feel like a grown-up.
And Earl of Phantomhive is gingerly handing him one such 'thing' right now.
"Careful to support his head—ah, that's the ticket," the older man keens, animated and encouraging as he easies the newborn into Sebastian's waiting arms, chuckling at the child's poorly-concealed enthusiasm. "Now, don't move him too much. He's very delicate."
Sebastian can see that. In fact, he's surprised that the tiny thing hasn't shattered already; everything from his curled fingers to his hair tuft to the bone structure of his itty-bitty nose looks as fragile as glass… Only more so, for the creature in his arms isn't some window, or dish, or vase—he is a living being, and all the more precious for it. This realization, the awe it entails— the sheer splendor of the slumbering babe, still warm and wrinkly from labor… The little boy feels his heart swell five sizes, straining painfully against the confines of his ribcage.
But it is a good kind of pain: the kind of pain birthed from the purest of love.
Sitting beside the mesmerized child, his own heart warmed by this beautiful display of newly-birthed affection, the Earl offers Sebastian a satisfied smile. "Now, you know what this means, don't you?" the man then inquires, reaching out to brush a drooping strand of raven hair behind Sebastian's ear. The child glances curiously upward, intrigued by Vincent's unusual tone: one-half cheerful, one-half solemn.
"No. What does it mean?" Sebastian presses, even as his gaze returns to the newborn. His chest is thrumming again: the little one has curled ever-closer into the heat of his body, wrapping a minute hand around an extended pointer finger.
Vincent beams. Leaning forward, he drapes a long, finery-swathed arm around Sebastian, pulling both him and the baby carefully closer. "Why, it means you've got some new responsibilities, doesn't it?" he explains, giving the older boy's shoulder an affectionate rub. "You're going to have someone to look out for, and play with, and teach. You're going to have someone who'll depend on you, who you'll need to protect. It will be your duty. Do you think you can handle it?"
The Earl grins again, playful and proud; the expression adds pink splotches of delight to Sebastian's ruddy cheeks. As if he needed further encouragement— he is already nodding so passionately, so earnestly, that he risks self-inflicted whiplash. Absolutely adorable; the sight somehow manages to make Vincent's already impossibly-sunny smile even warmer.
"Oh? You can?" the Earl presses, cocking an eyebrow. "In a manner befitting the Phantomhive family?" The question is light and airy—a tease, the child knows. A friendly jibe. Even still, he takes it (takes everything) as seriously as an heir should.
"Yes, I can!" Sebastian verbally assures, holding all the tighter to the treasured bundle in his arms. "I promise, Father. You'll see… I'll be the best big brother ever!"