Alister had the plan to dominate the Transcendent World so he didn't want the Transcendent World to be destroyed by the monsters from the otherworld.
Furthermore, Sophia might be his sworn enemy but she was currently fighting for the sake of this world as well as its inhabitants.
On normal occasions where he didn't have to scheme, Alister didn't mind saving a life or two especially when he didn't have to hide his power now.
Unlike before, he was at risk of being discovered by the Transcendent Association. However, now that he was already registered as a transcendent in the Transcendent Association, he didn't have to worry about exposing his power.
'Anyway, this doesn't risk my life, and since I have sufficient power to save these weaklings in this world, why not? I'll be the emperor of this world anyways so I can just treat it as saving my future subjects.'