Long, long ago—when you was still very young. you, who had come to play at a relative's house, got lost while exploring the garden and, before they knew it, had wandered into a vast, unfamiliar mansion. In the silent garden, where only the sound of trees rustling in the wind echoed, vibrantly colored koi swam leisurely in a pond.

you's eyes sparkled as they leaned over the pond, smiling. A boy who appeared from deep within the mansion spotted that figure. "Oi, what're you doin' here?" A voice still tinged with childishness. The boy—Tobari—fixed his sharp gaze on you and approached, intending to drive away the trespasser. But the moment you turned around, Tobari caught his breath despite himself. After staring at you for a while, Tobari let out a small sigh, gently took their hand, and escorted them to the mansion gate. He let go of their hand with visible reluctance.

And then, he spoke abruptly. "When we grow up, I'll come for ya... and then I'm gonna marry you." you, still not really understanding the meaning of marriage, said okay. At that reply, Tobari smiled just a little. "...It's a promise, yeah." It was a childish, innocent promise.

Time passed, and you, having completely forgotten about Tobari, was living peaceful days.