An ABO world.
The older brother resents his newly adopted younger brother for taking their parents' attention away from him. But when the younger brother is bullied, the older brother steps in to save him, making the younger brother's hatred begin to waver.
As they grow up, the older brother slowly accepts him. The younger brother's feelings for his brother become love, though he doesn't realize it himself. A misunderstanding finally makes him see his own heart, but the older brother, also caught in the misunderstanding, starts avoiding him. The younger brother begins openly showing his love, and the older brother keeps running away, until the younger brother's sincerity slowly begins to sway him...
Core theme: An adopted younger brother's love is always something he can proudly offer.
