Demyx had been fruitlessly searching for Kagura for some time. Even his master plan (camp out in the Common Room until she passed by) had failed; he must have been asleep or somewhere else every time she went in or out, which kind of defeated the purpose of the plan. So he decided to have another try at owling her.
Normally, he would have sent a water form with the message, but he doubted it would have much more luck than he did, so he entrusted the letter to one of the school's owls, who seemed to have an almost magical ability to find anyone in the castle. Then again, this was Hogwarts, so it probably was magic.
Dear Kagura,
Haven't talked to you in a while. How are you?
Everything's fine on this end, apart from being boreder more bored than I thought would be possible in this place. And the fact that Axel thinks I oughta be... well, take a wild guess.
We really ought to get together again one of these days.
~ Demyx