Thanatos doesn't say anything, but internally, he's surprised. He feels the keepsake do something, and it's a small reminder that the keepsakes can in fact fulfill their purpose. For all the effort he has put into the keepsakes and companions, there have been few instances of them doing what he intended. (Maybe his intentions were misguided in the end. Something he could think on much later.)

"You're not going to immediately return to your cabin to rest, so it's what I can do." He tries to keep his voice neutral even as he wishes that Ryo would do just that. It's a testament to earlier discussions (arguments) that Thanatos doesn't press further. Besides, the immediate danger has passed.

"Once things are settled here, I'll be in the dark quiet booth. Whatever happened there... I need sometime to be myself." Not exactly needing to be alone but not exactly needing company either. That is the kind of rest Thanatos will need.