The story is my experience and emotions. The girl starts first love for the first time, then she realises that she loves someone. (The flower language of lilacs is an requited love and the memory of youth.)
She only feels that loving someone is sweet. Then wisdom tooth begins to come out. But, the pain also comes with it. (In South Korea, wisdom tooth is called love tooth. When you love someone, love tooth comes out.)
She is aware of her requited love(A glove, a sock, a shoe and the collapse of the card tower), but the size of her love grows bigger and bigger (Blowing a balloon). A balloon means also immature love like childish.
She abandons her requited love, but leaves room for another love. Then she forgets the past love and start a new love. (The faded lilacs - the past love, Freesia - New beginning)