After so many years, the girl's feelings for the boy have finally undergone some small changes.
From the previous obedient calling of "Seiichi-nii" to the direct intimacy of "Seiichi Seiichi", and then to "my Aichi" as if declaring sovereignty, and then suddenly as if alienated, he became "Seiichi-senpai", and finally "Yukimura-senpai"
Is it the girl who has changed, or the boy who always wears a coat and always smiles?