Flirting
Nero kept his gaze fixed on Gabriel as he watched him drink the liquid from the vial. It wasn't that he doubted Gabriel's statement, but even so it would not hurt to be cautious. The thing that Nero was especially focused on was how Gabriel specifically knew what he wanted, whereas Arter had only reacted after he had been told what the vial contained.
They both knew about Liquid aether, but Gabriel seemed more familiar with it, as well as with Vaults. Considering how a new Vault hadn't been accessed in centuries, Gabriel's intimate knowledge of what it was and what it contained was noteworthy.
Nero watched as Gabriel closed his eyes after drinking from the while, a satisfied look on his face. Arter and Maximilian did not hesitate either, chugging down their vials.
It didn't take long. Only a few seconds later Gabriel opened his eyes, and upon discovering that Nero still hadn't drunk his vial gave him a curious look.