Guardians of the Lake

The Guardians of the Lake is the name given to a statue at a hot springs resort that depicts two lovers. It's based on an ancient legend about a young man who fell in love with a water sprite who lived in the lake.

But, there was a woman from the town that was also in love with the man. When she saw the water sprite with him, she got so jealous that she turned into a viscous monster and attacked everything in site.

The only way the young man and the water sprite could stop her, was to harness the power of their love to seal her beneath the lake. They used up all the energy in the process, rose up into the sky, and became two happy stars guarding the lake. The doomed woman was to remain miserable forever.

This story, however, was actually true. Evil Prince Darien released the evil spirit of the lake and it attacked Serena (mistaking her for the water sprite), her family also getting mixed up in the attack.

After Sailor Moon dispelled the Ancient Creature of the Lake, the woman rose into the sky to become another happy star.

Trivia

 * In the original Japanese version, the statue was called the "Legend of the Lovers" and the "water sprite" the man fell in love with was actually an angel that fell from heaven.
 * The statement of the lovers dying in the original was altered to only give an assumption without actually saying it.