Another theme could be the underdog. Since he's the little brother, he might be underestimated, but then he overcomes odds and shows that he's more than what others thought. This theme of defying expectations and rising above is quite common in stories. Also, the theme of family loyalty can be there. He, as the little brother, might be doing things for the sake of his family, which in turn makes him 'bigger' in the eyes of his family members and in the overall story.
One possible theme could be growth. The little brother might start out small and weak but grow in strength, character, or influence, becoming 'bigger' in different ways as the story progresses.
A third theme could be self - discovery. The little brother may be on a journey to find out his true potential, and as he discovers more about himself, he realizes that he can be 'bigger' in terms of his capabilities and contributions. For example, he might find out he has a talent for art or music that not only enriches his own life but also impacts those around him positively, making him a 'bigger' presence in the story.
Chapter 137, "Lai Fu's Death Has Another Cause", is the clearest early answer because the violence around Cause Jiang Li becomes final instead of hypothetical. A useful checkpoint is the way the scene starts with Jiang Li personally went to Lai Fu's tomb and performed a small...
Chapter 143, "How about Grandma introducing a girlfriend to you?", is the clearest early answer because it turns Princess Wen's situation into a concrete plot event. Early on, Is there really such delicious fish soup in the world?.
Chapter 342, "This is our Hua Country's archery", is the clearest early answer because it turns Daniel's situation into a concrete plot event. Early on, Some horses fell in the mud pits and never got up, some remained....
Chapter 27, "Signing Jiang Yan is fine, but you have to follow along too.", is the clearest early answer because it turns Shen Lan's situation into a concrete plot event.
Chapter 61, "Young Master Before vs After Going to the Countryside", is the clearest early answer because it turns Jiang Yan's situation into a concrete plot event. A useful checkpoint is the way the scene starts with Hahahaha, oh my god, Jiang Li's mouth is even more venomous.
Chapter 205, "The Fairy Descends to the Mortal World", is the clearest early answer because it turns Jiang Li's situation into a concrete plot event.
Chapter 128, "Which family created the white lotus persona to go transplant rice seedlings in the field?", is the clearest early answer because it turns Su Yinwan's situation into a concrete plot event.
Chapter 343, "He Can Support Jiang Li for a Lifetime", is the clearest early answer because it turns Lifetime Jiang Li's situation into a concrete plot event. The chapter turns that into something concrete by moving from But she suddenly acted mischievously indifferent, "Are you a...
Chapter 268, "I'm Just Jealous of Jiang Li, I'm Annoyed by Her!", is the clearest early answer because it turns Su Yinwan's situation into a concrete plot event.
Chapter 166, "Daniu Gets Jealous!", is the clearest early answer because it turns Zhao Lang's situation into a concrete plot event. It opens with Only after everyone in the small courtyard had left, did Zhao Lang...