The Weight of Immortality

"Kuro, don't you have any subclasses?" asked Mahiru.

"No," said Kuro. "Too… troublesome. The birth of a subclass happens when a person who is nearly dead or just died drinks sevamp blood… But, no one can tell if that human still wants to live, right? I don't understand and don't want to think about it. Too much trouble."

But is that the whole story? Or is Sleepy Ash holding something back? Something about his past and the kid he fished out of a river. Something about the family he found, and then… lost. About a past Eve who he almost made into a subclass, could have made his subclass… but didn't. And why?