XD THIS LORE IS GREAT!

So this is how Pentakill got it second start, thanks to Kayle meeting Karthus in Bilgewater after that band broke up (because Mordekaiser murdered a Freljordian crowd last time so they had to seal him and run for it) "She heard the depthless well of misery in his despairing lyrics and knew Karthus alone could understand her own sorrow. What followed was a drunken woe-off, a night of debauchery, gothic poetry and operatic singing that saw the men and women of the Slaughter Docks hurl themselves into the monster-filled ocean rather than listen to their maudlin duets. In the aftermath, Karthus and Kayle pledged the Vocalist’s Oath to return stronger than ever. After all, shared woe is better than solitary woe." so pretty much Kayle and Karthus have hooked up because both need the other's aid, and no one else can hear their songs and live past the end. XD

And on top of this, Runeterra also has Mount Olympus and HAD Atlantis (till Sona's songs accidentally sank it).