Different Worlds/ tanjiro(mermaid au)x reader

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Recap=

Your pov:

It's been 3 months now.  How time passes so fast.  You just wake up and boom, it's already the next month. These past few months have been great, I just finished high school {it was hell }  I was able to teach all three of them new things  science,literature, etc . It's quite funny seeing their faces of amazement watching a show on how stuff is made. Everything has been normal visiting levi once in a while. But does everything stay the same, I have this feeling I don't know how to explain it.

I really do love the company of tanjiro and nezuko as well as Zenitsu,  if I might say. Taking them to new places showing them the wonders and beauty of the 'human' world. I would tell them stories, they would tell me theirs. Who knew that the sea was so mysterious and  filled with secrets yet uncovered.

Tanjiro has told me about all the missions he has been on, defeating sirens, how muzan slaughtered his entire family and ended up turning nezuko into a siren.
'' and that's how me and nezuko joined the corps''
I lightly started petting nezuko's soft but silky hair.
''Wow, I am flabbergaste. I am  truly sorry about what happened to your family tanjro, you been through so much..'' I bring my head up and bring my eyes directly to tanjiro's.  ''no its ok y/n you don't have to feel bad, hey that happened long ago besides i have nezko with me'' he said with a smile  man not even I went through anything like that and i used to complain about life when I was in high-school.

"Don't feel bad for us,it was in the past. But hey, here we are, "
"I just feel dumb. You had it rough. You lost your family and only had one family member alive,I thought losing one person was hard.. but an entire family is crazy. "

June 1st year=??? 12:03pm
It's nice outside,summer is here. But I it just feels weird, like it's not real. The air is soft. The sun is out. **How wonderful** today is. "Y/n?" I turn my head around,  facing a man with red hair. "________?!" My eyes started to water, a feeling of grief filled my chest. "We're free y/n, free from him: the stranger hugged me. His face... I can't see it. It's blurred. "We are free y/n we can be together." I don't remember or ever recognize him, but I have this feeling I do. "Look for me in the future...." he smiled, a few tears rolled down his cheek  as he caressed my face.

"Look for me in the future, my love, promise me to do so.."

I shot up from my bed, my breath quickened, and my body was trembling. "Y/n, are you ok?" I bring my face up seeing my now opened door. Tanjiro. "Am ok, just a weird dream, nothing much."Hmm, if you say so,  do you want to talk about it?"

He walked closer now, entering my room, sitting down in the corner of my bed. He seemed sleepy.
"It's nothing bad. Like I said, it was a weird dream." He hummed in response."Couldn't sleep?" "Not really. " his head was down his mind in deep thought."
"I just feel like this is how do I explain. The past few months were a blast. " Was he nervous? "I have been seeing this place get crowded with these strange looking people in all white. They've been going around asking for stuff and information."
Strange people in white? Is he talking about scientists? Why would they be here.

"Where did you see them, tanjiro?" I frowned. "I saw them close to Levi's café" How strange..
"We have to stay low. We would want them to know your a-" "mermaid I know." I was cutoff. My eyes soften. "It's ok they won't do anything or even harm you in my sight" (foreshadowing goes crazy!)
"I- should go back. Nezuko is probably waiting for me." He laughed nervously. Walking out of my room, he closed the door.
Taking in a deep breath, I laied in the bed, staring at the ceiling. How did everything change fast.

Watching him leave the room a empty feeling filled my heart. Why? Why do I suddenly feel my heart heavy? Is it because of the dream?. The walls felt as if they are closing up on me. A thick atmosphere yet deadly,  one you can barely breathe and die by suffocating in it. Why. Did I change or is it just my imagination playing tricks on me. Why is it when I try to ask for help it just-. I hate being alone. I hate it. Why is it so suffocating here.
Crying to sleep won't help me escape anything anymore.

Why is it so hard to just be happy for a single day? Why is it so hard to smile all day and not cry. Why is it to fall asleep you have to cry. Why is it that when you cry you feel that empty feeling  A heavy feeling that makes you think stuff you never thought you can. A thought so endless,  powerful enough to take over one's mind. Yet they say they are normal when they are far from that. Is normal even a thing? Or is it just a word. Yet we keep on trying to persuade ourselves it's just a thought or one's imagination. When it's not. Why do I hurt. Why do I desire a feeling? A feeling I can't have in my hands. Sure I want to be able to feel it ,admire it. But why? Guess we will never know?.
*sighs*
"What am I even doing with my life."
I passed my hand along my hair. I finished school. Am not alone. But why do I feel empty?. "Ugh." "Looking around the room I seem to take in each and every detail. Plain and boring.
"How different is this world..why?" Deep thought huh?. Guess it's true what they say about them then. "It's so fucking empty and blank in this room, when was the last time I actually decorated the room." Laying down flat on the bed I stare up at the ceiling. Nothing changed after she left. "Oh grandma, how  life makes a turn." I never wanted to live a quiet life. Buy hey I got the trio with me...at least? They wouldn't leave me right.. not like how those movies are.. right RIGHT?