Thresh and Kalista's similarities -- The Souls
http://ddragon.leagueoflegends.com/cdn/img/champion/splash/Thresh_0.jpg
If you haven't noticed yet, Kalista is like my favorite character in terms of lore... What I wanted to discuss is the trend with some of the specter race on the Shadow Isles. Pretty much being like Kalista and Thresh, hecarim is a specter but I don't think he's looking to build up in souls.
Everyone should know that thresh's lantern hordes souls. Maybe this was something important in his past life. http://i.ytimg.com/vi/vkPsSmU1sEM/hqdefault.jpg
As with Kalista, when she took the guy's soul in her video(well both his and the invoker) it went to the spears protruding in her back. The spears are important to her because that is what killed her. Especially the one that stands out, The Black Spear. https://38.media.tumblr.com/5e375f54c2c9d4dc1f08dda7ad3cec37/tumblr_nfct12ld6g1sdk5d7o1_500.gif
So that makes me think that other specters that are interested in becoming more powerful. All have a certain item that they kept in death that horde souls. On the flip side, Kalista is definitely enjoying the power she get from it just like thresh is. Well maybe not enjoying, but the souls she collects are stuck in those spears. And I would think until she get revenge, they can't go anywhere. Kalista means just, but she is still just as twisted as thresh.
"Oh a betrayer? Where? Give me your soul and we shall get revenge.....so I can have his soul too! Then you will help me get revenge."
One of Kalista's quotes when your soul bound gets a kill "Yeesss, Punish the betrayers." So both Thresh and Kalista just horde Helpless souls in their important(undead?) items.
So I am going to say that the specter race are one of the many you dont want to meet from the Shadow Isles. They're humans who have been twisted. In thresh's case he was already twisted. Hecarim seems to have been a centaur in life, some I can't be so sure what his thing is. Karthus is a specter as well, but rather than hording, he tries to persuade. This is the similarity I wanted to talk about.