Seventh realm
At least in an ideal scenario, but that wasn't going to happen. Atlas would probably pursue his sister's killer to the end of time. It would take him a while to identify Kayden, but it would likely happen eventually. He just needed to consult the right people.
A time mage would probably be able to study the entire event and understand that Kayden killed his soulmate. Even with all the modifications to Atlas's soul, this would not stop him from chasing after Kayden. The boy had instilled ridiculously strong principles into Atlas's mind—honoring his family came before all other obligations.
"No, no, no, no," Jasmine was beside Athena's body, unable to do anything. Kayden had simply informed Atlas and then sat down, staring at Athena's corpse. He answered no questions; he just kept looking at his beloved's body.