This emoji is the 'koinobori,' a traditional Japanese decoration. They are flown in the sky on Children's Day, May 5th, to wish for children's health and success.

The carp is a symbol of strength and perseverance for its ability to swim upstream. It originates from a Chinese legend where a carp that leaps over a waterfall transforms into a dragon. Today, it's used not just to celebrate children, but also to mark the achievement of a difficult goal.