Actually, Riot's skill on writing Lore was really good. Check inside, really.

Kalista is known to carry Souls in search of vengeance that ply alliance with her spear. Good, we get into the Rift thinking Kalista is a good person. BUT SURPRISE She impales your sorry butt with her ghostly spear right in front of everyone. From now on, you are best friends forever. And she can throw you at the enemy team for maximum peeling. They say 'if the partner accepts the pact'. But you can't.

So grim, Riot.

Since start, there was no choice, only retribution.