Atsumu has known her since they were five. He doesn't remember how they met, but he remembers the beach. Maybe they met there. They had so many memories on the beach, where Atsumu had taught her how to play volleyball.
They were 15 now. She was beautiful. They have been dating since they were 12. Atsumu had asked her out on the beach.
She was perfect for him. He loved her (hair/color) hair, no matter the length. He loved running his hands through it. He loved staring at her eyes. They were a (eye/color) shade, beautiful in all lighting. Her personality was the (opposite/same) as Atsumu's. Together they would do everything possible.
"Let's go to the beach today." Atsumu suggested. He walked hand in hand with her. The beach was their favorite spot. The sand was always warm with the sun hitting it. The ocean was cooling, and always a vibrant blue.
They liked to walk the beach barefooted. Sometimes they'd enter the water and kick water at each other.
"Happy anniversary," she spoke softly as they walked down the beach. The tide splashed their feet. "We met 10 years ago, today, stilly." With her other hand she booped his nose.
Atsumu let a laugh out, "Oh. Happy anniversary." He then suddenly scooped the girl into his arms, listening to her laughs as he ran around with her in his arms.
"Atsumu, don't you dare!" She screeched as Atsumu ran into the ocean with her in his arms.
He pressed a kiss to her forehead, "Oops." He let go, dropping her into the ocean. As he was laughing, he felt a hand tug on him and he was suddenly under water as well.
When coming back to the surface, he heard her laughter- and it was beautiful. He shook his head, small sprinkles of water flying.
"I love you," he felt her cup his face. Before he could say it back, her hands went to his shoulders and he was shoved back under water.
"No fair!" Atsumu pouted, puffing his cheeks. "I was trying to be cute!"
She stuck her tongue out, "Oh, sweetie, that's pretty tough for you, isn't it?" Atsumu dumped her under water again.
"(Y/N)?" He called out when she didn't come back up. "(Y/N)?" He flinched, shutting his eyes, as he felt water hit his face. Wiping his eyes, he saw her laughing. "This isn't funny! I was worried!"
She continued to laugh, "It was very funny."
Atsumu led her out of the water, and the two of them left the beach to dry off. They went to his house, changing to new clothes, then cuddling on the couch.
He felt her fall asleep on his chest. Looking down, he smiled softly.
Everything was perfect.
She woke up an hour later. They ate dinner and went to the beach to watch the sunset. Tomorrow was Atsumu's birthday, and he was ready to spend it with her.
They sat up in the lifeguard chair, feet dangling. Her head laid on his shoulder, as his laid on top of hers.
"(Y/N)," he spoke, "you'll be with me tomorrow to celebrate my birthday, right?" He felt her move. She sat up, looking straight ahead. "(Y/N)?"
"Atsumu, you're leaving after tonight." She said, not looking at him.
The blond was confused, "W-What? Where am I going?"
"Back home." She looked at him, a smile on his face. "Where you belong."
"(Y/N)? What are you talking about. You've been to my house, it's a five minute walk from here." Atsumu reached to grab her hands but she pulled away. "I'm confused, tell me what's happening."
"You're finally growing up." She smiled brightly, tears gathering in her eyes. "And I'm so happy that you are."
"Of course I'm growing up, but what does that have to do with you not being able to celebrate my birthday with me?" Atsumu asked.
He watched as one tear slid down her face. "Do you remember how we met? When we got together?" She asked. He didn't reply. "Do you remember what I look like?"
"Of course!" He cried. "You have.." He looked at her, and she was a blur. He couldn't remember. He couldn't see her. "I..I don't remember!" He started looking around, noticing the beach was gone. "Where am I? (Y/N)?!"
"I'm here." The figure in front of him cupped his face. "And I'll always be, but you're going to forget all about me in a few minutes."
"You're my girlfriend, why would I forget about you?" He felt her wipe his tears away with her thumbs. "(Y/N), answer me!"
"Atsumu, I'm not actually your girlfriend."
With one blink, he was able to see her again. Her (hair/color) hair. Her (eye/color) eyes. Her (skin/tone) skin. Her beauty.
"You're lying! We've been dating for three years!" He cried out. He wiped at the tears that started to fall. "(Y/N), tell me what's going on!"
"I already told you, you're growing up." She smiled. "It was about time, you're almost 16. In one minute to be exact, and then I'll be gone."
"Where are you going?" He asked, voice cracking.
She smiled, two tears fell. "I'll disappear."
He didn't understand what was happening. What was she talking about. "(Y/N), tell me what's happening, please!" He cried.
"30 more seconds." She smiled. "I'm glad I was able to see you grow up. Thank you for bringing me along."
"(Y/N)?"
"10 more seconds." She cupped his face before leaning in for one more kiss. "I love yo-..." Atsumu had watched as she faded away.
Why did she kiss me?
Why did she love me?
What did she look like?
Who was she?
"Happy birthday, 'Tsumu!" Opening his eyes, he found his brother holding a bucket. He was shivering. He had poured water on him. "You don't look too happy."
(L/N) (Y/N)
"Who?" His twin brother asked. "Did you spend all night talking to some girl?" Osamu threw the bucket at him. "You seriously need a proper sleep schedule.
"What do you mean?" Atsumu blinked. "We know a (L/N) (Y/N), don't we?"
"Talking about your imaginary girlfriend again?" His mother and father had appeared.
Imaginary?
"Ah, I remember when you made her up when you were five. You were attached to her for so long." His father laughed. "Osamu, remember when he was 12, he said they were dating?"
"Yeah," Osamu laughed. "But obviously, Atsumu grew up."
"You're finally growing up."
Atsumu inhaled. It was all an imaginary world. Everything he's felt. It was never there in the first place.
It was just some paracosm.
