Honkai Star: Rail x Reader Oneshots

"I'd do whatever I could do" | Boothill x Reader x Aventurine

Summary: Aventurine undergoes a bizarre transformation, reverting to his child form due to an inexplicable force. In this new, vulnerable state, he is found by Boothill, and you, who instinctively offers comfort and protection. Together, you three form an unlikely family, as Kakavasha, now a child, grapples with his new reality, experiencing innocence and care for the first time. Amid the chaos of the universe, they find brief solace in their newfound bond.

Tags: Aventurine x Reader x Boothill, Platonic, Transformation, Family, Unexpected Bonds, Comfort, Childlike Innocence, Humor, Surreal, Reader is called Mother but not implied female.

Warnings: Transformation (age regression), confusion, mild existential themes, emotional tension.

The warm glow of the sunset outside the IPC headquarters bathed the sterile interior in a soft, amber light. Aventurine leaned back in his chair, his fingers tracing the edges of the holographic charts laid out before him. The evening had been unusually quiet—until the unexpected wave of dizziness hit him.

"Not again..." Aventurine muttered under his breath, rubbing his temples as his vision blurred momentarily. He had always been one to trust his luck, but this felt… different. A strange sensation, something he couldn’t place, rolled through him like a tide. His body stiffened, a soft jolt running through his spine.

Before he could even register what was happening, the world around him began to warp. The walls seemed to shift, colors blending, and the floor seemed to fall away from beneath him. He gasped, feeling an overwhelming pull, and in a split second, his adult form began to shrink, his limbs dwindling down to a child’s size. His once confident stance faltered, replaced by a wobbly, unsteady posture.

Aventurine, now no longer the calculated and sophisticated man he had been moments ago, stood frozen in the middle of the room. His attire—elegant, composed—hung awkwardly around his much smaller frame, the fine materials pooling like a blanket on the floor. His golden-rimmed glasses fell from his face, and his typically calm and collected features now bore the unguarded innocence of a child.

The air was thick with confusion. Aventurine’s eyes—now large and wide—darted around in panic. His small hands trembled as he reached up to touch his now-short(?) hair. “What…?” he squeaked in a voice that was much higher than he had ever remembered it being.

Before he could further process what had happened, the door to his office slammed open, and in strode Boothill. The cyborg cowboy, tall and imposing, paused at the threshold when he saw what was unfolding before him. His mechanical eye whirred, analyzing the situation, his black pupils narrowing in confusion.

"Well, ain’t this somethin’," Boothill muttered, taking a step forward. His usual bravado faltered just a little as he looked down at the small, confused child now standing where Aventurine had once been. "Ain't no way I’m seein’ things right now..."

Aventurine—no, Baby Kakavasha—looked up at the towering cowboy. The child’s eyes were wide with fear, but there was also a glimmer of recognition. His lips parted as he searched for words, but none came.

Boothill stared at him for a long moment, his gloved hands hovering near his holstered guns as if unsure what to do next. “What in the galaxy is goin’ on here, kid?”

The air felt thick with tension. Baby Kakavasha took a hesitant step forward, his small voice trembling. “I—I don’t know,” he stammered, struggling with the unfamiliarity of his child’s body. “I didn’t do this. It wasn’t me.”

Boothill scratched his head, his mechanical parts creaking as he did so. “Kid, I ain't got the faintest clue what’s happenin', but one thing’s clear—you ain't lookin' like yourself. You a shape-shifter, or is this some kinda joke?”

“Please,” Kakavasha’s voice was softer now, more fragile than the usual sharp tone he carried as Aventurine. “Can you help me?”

Boothill exhaled slowly, his harsh features softening just a fraction. He wasn’t the sentimental type, but seeing this child—this version of Kakavasha—made his heart tug with an unfamiliar feeling. He took a step forward, crouching down to meet the small child’s gaze. “Alright, kid,” he said with a sigh. “Guess I’m gonna have to step up. I ain't got no clue how this happened, but you're not alone in this.”

Just then, the door to the room slid open again, and you stepped in. Your instincts kicked in immediately, and your brow furrowed at the sight before you. Aventurine, or rather, Baby Kakavasha, looked up at you with wide, uncertain eyes, his small body trembling in confusion.

Without hesitation, you approached him, kneeling beside the child. There was no explanation for why, but an overwhelming urge to protect him, to care for him, surged through you.

“Don’t worry,” you said gently, extending your arms to comfort him. “You’re safe now. I’ll take care of you.”

Boothill, watching the scene unfold, couldn't help but feel a sense of protectiveness welling up in his chest. “Guess that makes me your dad then,” he remarked dryly, scratching his head. “Ain't no way this is normal, but looks like we’re a family now.”

Kakavasha blinked at Boothill, still overwhelmed by the bizarre circumstances. “Father?” he echoed, testing the word on his lips. His expression was a mix of confusion and surprise, but also... curiosity. “You’re... my dad?”

“Yeah, you heard me right. I’m your old man now,” Boothill said with a smirk, though there was a softness in his voice that he didn’t usually show. "Ain't that somethin’, kid?"

Kakavasha took a moment to absorb the idea, his little mind scrambling to make sense of the situation. His usual sharp wit was clouded by the childlike innocence that had taken over his demeanor. “So, uh... does this mean I can have cookies for breakfast now?” he asked, his small voice high-pitched but filled with a strange, hopeful tone.

Boothill blinked. "Well, uh... sure, kid. Why not?" He shook his head in bemusement. "You're supposed to be some kinda stone-cold strategist, and now you're askin' about cookies."

Kakavasha grinned widely, the simplicity of the question almost making the chaos around them feel a little more manageable. “Maybe... maybe we can even get ice cream after dinner!” he added, his face lighting up at the thought.

Boothill snorted, leaning back on his heels. “This whole thing’s a mess, kid, but sure. Ice cream it is.” He shot a glance at you. “You’re okay with that, right? I mean, we're a family now... I think?”

You chuckled softly at the absurdity of it all. "Sure, ice cream sounds good. After all, you’ve got to ease into being a kid again, right?"

Kakavasha looked up at both of you, his expression shifting from bewilderment to something softer, warmer. Despite the situation being entirely out of his control, there was a sense of comfort slowly building in him. Maybe, just maybe, this odd, unexpected family would be able to piece together a bit of stability, even if only for a moment.

“Thank you,” Kakavasha whispered, his voice now tinged with gratitude. “I... I don’t know what happened, but... I feel like I’m not alone anymore.”

Boothill’s face softened, just a little, as he placed a hand on Kakavasha’s small shoulder. “You’re not alone, kid. No matter what happens, we’ve got each other.”

The improbable new family stood there for a moment, in the midst of the swirling chaos, unsure of how or why this all came to be. But for now, Kakavasha was no longer a vengeful adult filled with hatred. He was simply a child, embraced by a new, unlikely mother and a cyborg cowboy who, in this strange turn of fate, had somehow become his father.

And for a brief, fleeting moment, the chaos of the universe outside seemed to fade away as they stood together, a family of three, with Kakavasha’s small hand resting gently in Boothill’s rough palm. The game of life had thrown them a curveball, but for now, they would face it as one.

The dawn would come for them eventually. But for now, they had each other. And cookies. And ice cream.