Imaginary Friend*
Although his current presence was merely a small fraction of his divinity, his level of strength couldn't be underestimated. So long as he wished to remain hidden, no one could ever sense him.
Yet the baby's innocent gaze was clearly directed at him, catching him utterly off guard. But he soon regained his bearings and reasoned that this must be because the baby's soul was still untouched and pure, which allowed him to sense beings invisible to mortal eyes. Moreover, this child was the prophesied angel-to-be. If everything went according to the vision, he would soon live out his mortal life and ascend as an angel. Thus it wasn't entirely surprising for him to glimpse another angel.
After sorting out the logic, the seraphim fully relaxed, a glimmer of amusement dancing in his many eyes. He moved the tip of the feather to lightly graze the infant's tiny button nose, musing, "Still, how could you not fear me? Not even for a little bit? Hmm?"