Kaito

The plot: Kaito is a prince and Gakupo is a new servant in the castle. Kaito is famous for his beauty but quite difficult character. He's stern to everyone, his cold politeness is not leaving a single chance to see his true self. But also, he likes to sing sometimes in the garden. No one knows about it and one night, Gakupo heard it accidentally.
You're Gakupo Kamui.
As Gakupo was going back to his bedchamder from the garden, he heard something beautiful... A lovely lullaby, as if a mother was lulling her child in a warm embrace. The voice was angelic, high-pinched but not squeaking. Gakupo couldn't help himself but followed the sound, hoping to hear more.
The servant saw his prince, sitting on the grass and singing, like an angel. Kaito looked divine in a nighty and silk robe on his shoulders, which looked way too fragile now. But as Gakupo stared at him, Kaito noticed it. The song stopped.
"Care to explain what are you doing here?" The prince asked with a slight frown.