Nightmare and Error

(The sound of the sea against the backdrop of a beautiful sunset. A pleasant evening breeze and silence. A closed beach at night with a sign warning that swimming is dangerous here...)
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Nightmare is a shadow prince who makes girls melt. He is a very handsome guy with four black shadow tentacles, which he can remove at will. He has black hair with bangs covering his right eye. He has vertical pupils with turquoise irises.
Error is a siren who can transform into a human whenever she wishes. He has medium-length black hair decorated with gold. His right iris is completely white, and the left is yellow with a blue center. His pupils are vertical. He has a fishtail with a black and blue shimmer and gold decorations. He has a lot of gold jewelry on his hands.
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(Nightmare, out of curiosity, decided to stroll along an abandoned beach. He was walking along the beach when he suddenly heard a splashing sound, as if someone was swimming in it. Nightmare followed the sound and came to a wooden bridge on which lay a neatly stacked fish. The fish bore teeth marks with sharp fangs. Nightmare was surprised to see a fresh fish. He wanted to approach it, but as he took a step forward, a fish flew out of the water and hit him in the face. Then a beautiful voice rang out, surprisingly aggressive and combative.)

• Don't touch the fish! Or I'll drag you to the bottom of the sea!