Mayflies live only a day as adults, but blue whales live for decades.
What do you want to express?
If a mayfly falls in love with a blue whale, it is not terrible, because its life span is short and it will leave the world soon.
Well, sometimes a short life can be considered a lucky thing...
But what if a blue whale fell in love with a mayfly?
Intention: Fall in love when it's time to fall in love