Older brother, younger brother
His younger brother surpasses him in ability. Not just in poetry- Goujun has no pretensions to any talent there- but in diplomacy, in statescraft, maybe even in strategy and warfare as well. Gouen is quite unaware of this fact; or if he does know, keeps that knowledge so far from his manner that it looks exactly as if he doesn't. That's one reason among many that Goujun loves him so well.
His older brother is high-strung and moody: lashing out in anger, plunging into despair, plagued by sensitivities to things Goujun can't even see. Any complaints Goujun may have made in his childhood about Goushou's unfairness were checked at once, and severely, by the oldest of them. Goujun bowed his head and waited to see if he might in time understand his ani-ue's wisdom. In time he did. And, now that there will never be more than the four of them, is grateful that there is one brother weaker than himself, one who depends on his strength and wisdom to supply the deficiencies of his own. Goushou is quite unaware that's what he does, which lets Goujun go on doing it without awkwardness. That's the other reason Goujun loves Goushou.
Why drabbles? Partly of course because they're the one form where one may legitimately tell, not show. This makes them invaluable as a form of character meditation, clarifying things for use in later long fics.
Partly because they're like those art book plates, "detail of The Nativity with Magi"- the close-up that calls your attention to the little knot of wildflowers growing to the side of the stable when in the full painting your eye is too occupied with the gold-cloth'd kings and their servants and the holy family itself to see it. The telling character touch, the concise dialogue, may go unnoticed in the sweep of plot in a full story, but the drabble points it out to you.
Sometimes it's just technical virtuosity: that hardest of things, meaning implicit in the blank space and the thing not said. In a full story it takes a sensitive reader to notice what an author doesn't say; in a drabble it's an unavoidable part of the form. Equally from the pov of writing the things: you have to select not just the fewest necessary words but also the fewest necessary details, the ones that will convey the most information and indicate most clearly all the things you aren't saying. Not-saying is an art, and not a natural one for me, at least, though I gather it's the language a lot of people speak. Drives me mad; not-saying IME only works when I know the people well enough to know what it is they aren't saying. Family, is what that means. Otherwise there's the not-saying that has meaning because what someone's likely to be thinking is so commonplace that I already know it from context: which is always more likely than the other kind and, alas, more likely to be said as well.