He didn't swim through it
"What....w-what are you doing..."
( i am so sorry that i left you like that, i was going to rp with you for the night but then, for some reason, parents took my damn chromebook, i promise when i get back from school i will TOTALLY rp with you again! ;w;)
"JUST...go, i don't have the strength to kill an innocent person...i'd rather be shunned anyways..."
"I....every prophesy has-a catalyst. Something that pulls me to it-literally. And in this case...it's you."
Siren saw a glowing orb at the center of Kappa's chest, a thread of energy flowing outward from it and connecting him to Siren.
"...If I try to escape...I-I'll just end up getting pulled back-"
It faded away on it's own, though still present-
"It's more like I'm connected to you. You could go wherever you want-I'd just get pulled along with you. I mean...I-I've tried to escape prophesies before...but usually I can't swim very far from the catalyst before I get pulled back...and it's because you're....y-y'know....meant to kill me....?"
He gestured at the abandoned spear