Their first meeting took place when he had his first-ever training from Genma. The last thing he remembers is his father throwing him from the tenth floor.
It's already dark when he regained his consciousness. Is it night already, his four years old mind thinks? So dark here, wherever this is. So when he saw the light, he tried to go to the light. But someone stopped him. That someone is Death. But he doesn't know that yet at the moment.
"No, this is not your time to go there yet."
"Who're you?"
"Me? I'm being known as Death, Ranma Saotome."
That is the start of their friendship.