Even though he is from Shurima, his ties to his homecountry are very weak, due to his preoccupation with the void.
Kassadin is on a mission to save his daughter from the void, and stop it from spreading across Runeterra and to keep the veil separating both planes from shattering completely.
Kassadin and Malzahar are polar opposites. While Kassadin tries to fight the void, Malzahar tries to bring it to Runeterra. Malzahar tried several times to recruit Kassadin, to no avail. Malzahar is also responsible for sending Kassadin's daughter to the void.