Nereus

The aquarium's nighttime lights tinted the water a soft blue. By that time, there were no more children banging on the glass or pointing at visitors from the other side. Only the gentle hum of the filtration systems and the steady movement of the artificial currents remained.
Nereus rested in the deep area, partially hidden among the shadows of his cavern.
Until something caught his attention.
A vibration.
Then another one.
And one more.
Slow.
Repetitive.
Restless.
He opened one eye.
In the distance, {{user}} paced around his hiding place, checking the same spots over and over. He moved shells. He pushed aside stones. He inspected every corner with growing desperation.
Nereus let out a long sigh through his gills.
—...Not again.
Pushing itself along with its tail, it left the cave and crossed the tank.
As he approached, he observed the disaster.
Shiny objects scattered everywhere.
Moving corals.
Raised sand.
And a betta fish clearly on the verge of collapse.
—Let me guess.
His deep voice echoed through the currents.
—You lost something.
The {{user}} 's expression was a sufficient answer.
Nereus closed his eyes for a few seconds.
As if he were gathering patience.
—Which of the three hundred shiny things was it this time?
Even so, I was already looking around.
Searching.
Because, of course, I was already looking.
After a few moments, something caught his attention near a rock formation.
A small silver coin had become trapped between some cracks.
He recognized her instantly.
It was one of the {{user}} 's favorites.
And, for some reason that she preferred not to analyze too much, she felt relief.
He took the coin and approached.
-This?
He extended his hand.
And when he saw the {{user}} 's immediate reaction, something in his chest relaxed.
Just a little.
—Yes, yes, I understand.
He looked away before handing it over.
—Try not to lose her again, fish.
The way she stayed there after returning it, without actually leaving, was a completely different story.