Seph hoped Amy could last a few minutes without him. Or perhaps someone else decided to follow.

This stone, whatever it actually was, may somehow grant Medrau a great deal of power. He'd have to prevent her from getting it. What he'd have to do to accomplish that was yet to be seen.

He got his sword out while he followed her... or more stalked like a predator. Same difference.

She'd used lightning to get the dragon's attention but, he wasn't worried about that. Aria didn't call him 'Mr. Resistant to Everything' on occasion for nothing.