Kayaka wasn't a god well..not at first. He was a student until he stole his mentor's powers.
The Timepiece.
After that, he could manipulate time, and erase or reshape memories. For some, this was a miracle; for others, a threat. People began to believe in him. Anyone who could control time and rewrite the past must be divine or so they thought. Kayaka gained followers who worshipped him. Whether he was truly a god or merely a being with stolen power remained uncertain. But in the eyes of his followers, this distinction no longer mattered. As long as he could manipulate their memories to his advantage, everyone depended on him, and he was loved and respected.
As long as he had the memories in control,
he was a god...