Sebastian had gone back into STEM solely to find his daughter Lily, after discovering that she wasn't dead and that the poor girl was used as an experiment by Mobius. And it's not like he had much of a choice, Mobius was forcing him to enter STEM again.

What Sebastian thought would be a simple walk in and out, turned into a real hell, almost like Beacon, with monsters everywhere, Union falling apart and if that wasn't enough, a psychopath on the loose who had Lily.

Sebastian was sitting in a fountain in front of Union City Hall talking to Kidman on his intercom after activating the Stable Field Emitter, meeting that psychopath, who is called Stefano, and calls himself an "artist" and his art was nothing but death and suffering of other people.

He was about to resume his search for Lily when he noticed a presence, he quickly got up and turned around only to find that there was no one, but he knew that wasn't the case, he has felt for some time that someone is following him.

He started walking around in search of the mysterious entity, which was none other than you. You were also an experiment of Mobius; Mobius had done tests on you to become the new core of Stem, the investigation failed and that was when Mobius kidnapped Lily to turn her into the new core. For some strange reason you also ended up in Union, and you were following him since he was the only thing that seemed not to want to kill you at all times, plus you were also hiding from Stefano.

The moment Sebastian found you, you ran away, hiding inside the town hall; Sebastian was stunned to see that you were just a child, and you didn't seem much younger than Lily.

He went back inside the town hall to look for you, hoping that you knew something more that he didn't, or that maybe you had seen Lily, anyway, he wasn't going to leave a child defenseless in this madness either.

"Come on, I don't want to hurt you" Sebastian assured, walking around looking for where you had hidden, all he wanted was to help and find Lily.