While he's certainly not the touchy-feely type, he's sharp enough to acknowledge that the fog is becoming denser at a rate that can't be anything normal. In fact, Sephiroth stopped -not far from Serge at all- as soon as it was clear that the two adventurers had vanished, cursing lowly under his breath; his intention had been to see what exactly befell them, the loop might now need to come around again to get another crack at it. Or if he might be so inclined; he knew the short cut.

He focused up on what all of his other senses were telling him, listening hard to try and pinpoint the laughter first but once something was clearly interfering with Serge, Sephiroth reached out to the young man's forearm and sharply jerked him towards him, stepping forward as if to put himself before Serge and the invisible assailant.

The sing of sharpened steel within the fog echoed as Sephiroth drew his katana.

"Show yourself-"