They are brothers and love rivals, "fair competition" for the girl they like.
Six years old,
"Yu, I like her too, please! Just give it to me!"
"Get out!"
Eighteen years old,
"Yu, long time no see. It turns out you like her too. Seeing that so many people like you, just give it to me!"
"Get out!"
Twenty-three years old,
"As the saying goes, competition and cooperation lead to a win-win situation! Little Yu, let's find a way together!"
"Get out!"
Twenty-eight years old,
"Yu, you're not young anymore, so don't argue with me."
"Dove... Well."