"Every night you can keep or change the target." Being a child of Night means a lot of night related things.

"I..." Thanatos pauses. He didn't think about that because keepsakes were usually kept on a person... but it's a really good question. He goes over how he imbued the keepsake with his power. "No, I don't think so. It depends partly on your connection to your target. Without you, the connection can't be completed."