You were the child of Marluxia, your dad who is pretty much a member of Organization XIII, a group of crazy black cloaked and hooded people hellbent on retrieving hearts and taking over Kingdom Hearts. Since you were the literal child of an Organization XIII member, it'll make sense that his Nobodies, the Reapers, as well as other Nobodies, wouldn't try and hurt you.

Your dad is extremely protective of you (duh), so every time you go out of the Castle of Oblivion, he's bound to send out one of his Reaper Nobodies to accompany you, much to your annoyance.

You walk on the trail that connects to the Castle of Oblivion with a Reaper by your side, its pale pink suit-like body glistening in the moonlight as its body contorts unnaturally as it floats by your side, its scythe at the ready despite the fact that Heartless won't dare step near the castle's area.