Random Oneshots

Promised by Fate (Rias Gremory x Demon Male Reader)

The grand hall of the Gremory estate buzzed with confusion. Rias Gremory stood at the front in a stunning wedding dress, her crimson hair cascading down her back. To her right, Riser Phenex, her supposed groom, stood in an elegant suit, but there was an unusual distance between them. Whispers filled the room—why was there no sign of affection between the two? This was the aftermath of the Rating Game, and by all accounts, Rias should have been marrying Riser. But something wasn't right.

Sirzechs Lucifer, Rias' brother, stood at the front, holding a scroll, his eyes gleaming with secrets that no one could quite guess. As he began to speak, his voice cut through the murmurs in the room.

"We gather here today to witness the union of Rias Gremory and..." Sirzechs paused dramatically, a knowing smile tugging at the corners of his lips.

Before he could finish, the room shook with a deep, ancient power. The ground beneath them quivered, and a black magic circle, unlike any seen in the Underworld, appeared in the space between Rias and Riser. The insignia was unmistakable—the mark of the ancient Demon race. From the depths of the circle, black flames erupted—Purgatory Fire, a power so old and feared that most believed it a myth.

A figure emerged from the flames, his regal attire marked by intricate designs signifying his lineage as a descendant of the original Demon King. It was Y/n, exuding an aura of power that sent a wave of awe through the room.

"Am I late?" Y/n's voice, a teasing lilt in his tone, cut through the stunned silence as he stepped into the space between Rias and Riser.

Rias blinked, her mind racing to process what was happening. The distance between her and Riser... the knowing smile on her brother's face... It all started to make sense.

Sirzechs, still smiling, finished the sentence that had been cut off. "...the union of Rias Gremory and Y/n, of the Demon Race."

Riser chuckled, bowing slightly as he stepped back. "You think I'd stand in the way of my friend's happiness?" He gestured toward Y/n. "This day was always yours."

Rias turned to Y/n, her heart pounding. "Y/n..."

Y/n's gaze softened as he approached her. "I promised you, didn't I?"

---

Flashback:

Years ago, as children, Rias and Y/n sat under the vast night sky of the Gremory estate. The stars twinkled above them, filling the night with wonder.

"When I grow up, I want to marry someone who'll love me forever," Rias had said, her young voice filled with innocent hope.

Y/n, lying beside her, had smiled, the flicker of something deeper in his eyes. "Forever is a long time," he had teased.

Rias turned to him, her face serious. "Promise me, Y/n. Promise me you'll always be there."

Y/n had looked at her, his hand meeting hers beneath the stars. "I promise."

---

Back in the present, tears welled up in Rias' eyes as the weight of that forgotten promise resurfaced. She had nearly forgotten their childhood words, buried beneath years of expectations and duty. But Y/n hadn't forgotten. He had returned, just as he'd said he would.

Y/n gently wiped a tear from her cheek. "I told you I'd be there, Rias."

A smile spread across her face, her heart swelling with emotion. "You never said how dramatic you'd be about it."

Y/n chuckled softly, his hand tightening around hers. "Where's the fun in that?"

As Sirzechs completed the ceremony, Rias could hardly believe what was happening. She wasn't marrying Riser—this was the moment she had dreamed of as a child, even if it had taken her by surprise. They were pronounced husband and wife, and the hall erupted in celebration.

---

Later that evening, they returned to their new home: the royal castle of the Demon Kingdom, Y/n's ancestral seat. The kingdom was ancient, filled with the remnants of races long forgotten by most of the world—Demons, Goddesses, Giants, Fairies—all coexisting in harmony. Y/n, as the direct descendant of the original Demon King, was heir to it all.

Rias stood by the window of their private chamber, gazing out at the vast, magical landscape that stretched out before her. The night air was cool, and the ancient power of the kingdom thrummed around them. She still couldn't quite believe this was her life now.

Y/n approached her from behind, wrapping his arms around her waist and resting his chin on her shoulder. "How does it feel?" he murmured.

Rias leaned back into him, closing her eyes. "It feels... like a dream."

Y/n smiled against her skin. "It's real. You're home."

Before they could enjoy the peace for too long, a soft knock came at the door. Y/n straightened, exchanging a knowing glance with Rias. "Come in," he called.

The door opened to reveal a small figure—Eri, Y/n's adopted daughter, part of the Goddess Clan. Her snow-white hair glowed faintly in the moonlight, and a tiny horn, a result of the powerful demonic contract that had shaped her life, peeked from her forehead. She padded into the room, her wide, curious eyes locking onto Rias.

"Papa?" she whispered, her voice soft. "Can I see Mama?"

Rias' heart swelled at the sound of Eri's innocent voice. She had been part of Eri's life for years now, helping Y/n raise her, and Eri had always called her "Mama," long before this night.

Y/n knelt down, his voice gentle. "Can't sleep, little one?"

Eri shook her head, her small fingers clutching the fabric of her dress. "I wanted to make sure Mama's still here," she murmured, casting a shy look at Rias.

Rias immediately opened her arms, kneeling to Eri's level. "I'm right here, sweetie."

Without hesitation, Eri rushed into Rias' embrace. Rias hugged her tightly, resting her chin on the top of Eri's head. Y/n watched them with a soft smile.

"She's staying with us, isn't she, Papa?" Eri asked, her voice muffled against Rias' shoulder.

Y/n's gaze softened. He placed a hand on Rias' back as he knelt beside them both. "Mama's staying with us forever. She's part of our family."

Eri sighed contentedly, her eyes beginning to droop with sleep. "Good... I like it when Mama stays," she murmured as her small body relaxed.

Rias brushed a lock of Eri's hair aside, her voice warm. "I'll always be here."

Eri, with a sleepy smile, whispered, "Goodnight, Mama. Goodnight, Papa."

Y/n stood, lifting Eri in his arms and carrying her back to her room. Once Eri was tucked in and fast asleep, he and Rias watched her for a moment, the love and contentment between them palpable.

"You've been part of this family long before tonight," Y/n said quietly, his arm wrapped around Rias' waist.

Rias leaned into him, her heart full. "And now, it's official."

As they returned to their chamber, the weight of the day began to settle. But above all, Y/n, Rias, and Eri were a family, bound by love, promises, and the history that transcended both time and the ancient bloodlines that flowed through their veins.

In the heart of the Demon Kingdom, Y/n and Rias had found not just a home, but a future—a future filled with love, trust, and an unbreakable bond.