Su Nuannuan is a fan of Doraemon. Because she is extremely obsessed with Doraemon, she is nicknamed: Su Doraemon.
Sun Daxiong's real name is Sun Chenghao, and he got his nickname precisely because he disliked Doraemon.
When Su Nuannuan and Sun Chenghao were forgotten light years away, everyone only remembered Su Duola and Sun Daxiong. In fact, they were both lonely children.
When Su Duola met Sun Daxiong, when Su Nuannuan met Sun Chenghao.
They were still lonely, so lonely that they only had each other.
"I may not really like Doraemon, but I really like you." - Su Doraemon
"Whales are the concern of the deep sea, you are my concern." - Sun Daxiong
The whale is the worry of the deep sea, loneliness is the worry of Su Duola, and Su Duola is the worry of Sun Daxiong.