For him to endure the overwhelming mind and body suppression on the Second Floor, he has to reach the Aspirant Supernal rank first. Only then would he be strong enough to roam—and find a Nightborn that was willing to get to know him.
Back then, he was reckless and paid dearly for it.
Now, he was an Aspirant Supernal.
Enough to roam the Second Floor without being suppressed, but he decided not to.
Kai is the First Son of the Primordial Night, and this was the House of Night, his own domain.
If he backed away and let others handle his situation in his own domain, then that would be a disgrace to himself, his siblings, and the Goddess of the Primordial Night. For that, Kai decided to handle this situation on his own.
He walked out of Noxian's domain again.
Behind him, Noxian could only watch as he walked away without saying what he was going to do.
Kai continued onward into the darkness.
He didn't need to look behind him as he knew Noxian would've followed him.
