I really admire the concept that both, Hira and Kiyoi are flawed characters with many insecurities and self doubts and what mystifies me is that their love story is like that 'adorable yellow duck'in that 'gutter'.

The romance that bloomed at the least expected place of life.

Also i love another symbolism that yellow duck in the gutter part holds.. the part where kiyoi sees that duck floating in the gutter and says nobody cares about that yellow duck while literally on the other side hira's taking the picture of that duck admiring it to the fullest. That's what summarises beautiful man for me.