Nagasumi's older sister a Shark Fujishiro x reader

The begining

Idk what you call it but you are a mermaid shark! Also imma change the story line so Nagasumi does drown but there is a storm that causes him drowning.
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You and Nagasumi were playing at the beach while your parents were sitting far away from you guys, "Let's go into the water (Y/N)!" Nagasumi yelled to you as he dove into the sea. "No thanks I'll stay here!" You replied because you didn't want for anyone to see that you were a mermaid, you don't know how but you are a mermaid. You had gone home for the day with Nagasumi by your side and your mother and father walking in front of you guys. Your parents discovered that you were a mermaid when you were born, you had a shark tail! They didn't disown you because you had a tail in fact they helped you and encouraged you to not think you were a freak with a shark tail. As you got older your mermaid form changed, your skin became a light grey and your eyes became a glowing yellow. When Nagasumi found out he wet you to test it out, once he saw your mermaid form he didn't scream he just looked amazed! So your life was going easy so dear while visiting your grandma in Setto, she had known about your mermaid form too and told you stories of other mermaid sightings in the ocean. Right now you and Nagasumi were listening to one of your grandma's mermaid stories while your mother and father were asleep, "There are others like me?" You asked your grandma wide eyed, "Yes child, eyewitness reports saying that they have seen mermaids by fishing nets or coral reefs." Your grandma said. "Wow!" Nagasumi said "Lets go to the beach tomorrow! Maybe we can see one (Y/N)!" Nagasumi said excitedly. "Ok we can ask mom and dad." You replied to a happy Nagasumi, "Rest kids for tomorrow." Your grandma said as she stepped out of the room. "Thank you grandma!" You and Nagasumi said in unison.
{TIME SKIP!!🎐}
You and Nagasumi were running down to the beach while your parents were trying to keep up behind you. "Kids slow down!!" Your mom said while catching her breath. "WERE HERE!!" You and Nagasumi yelled while he jumped in the water. "Hey little bro imma go to the rocks so they can't see me!" You yelled to Nagasumi, "Ok sis!!" He yelled back. You laughed at his silliness and walked to a small cave covered by rocks, you sat down and put your legs in the water to have you transform in the cave. You looked up at the sky through the opening in the cave's roof, you noticed that the sky was getting a bit grey. You dried your legs and went outside the cave to tell Nagasumi to get out of the water, but when you got outside you saw Nagasumi drowning in the raging water. You freaked out and wanted to save him but you couldn't risk it "NAGASUMI!!" You yelled to him to maybe calm him down. He saw you and yelled "HELP (Y/N)!!" That's until he went down under. "NNOOOOOO!!" You screamed as you fell you your knees, it started to rain so you went back into the cave. You cried until the storm subsided then you went outside, to your suprise you saw Nagasumi sitting drenched on a rock rubbing his head. "Nagasumi!!" You yelled as you ran to him with open arms, "(Y/N)!?" Nagasumi said as he turned around. You engulfed him in a bear hug and checked him for any injuries, "(Y/N)?" He asked as you suddenly stopped, then he saw you sniffle. "I'm sorry" You said barely above a whisper. "It's ok" Nagasumi said while hugging you. You both kept hugging until you saw a shadow of a man with an afro above you and Nagasumi. "Who are you?" Nagasumi asked before you both were knocked out.