[Eichi will... treat him like a pet, carding his fingers through Tenn's hair, petting him gently but with an air of ownership. And since Tenn is a pet- he should be dressed like one. That is, undressed as he is, but also there's that collar that Tenn brought.

So Eichi is swift enough, picking up that collar and leash and beginning to fit it on Tenn's neck. He makes sure it is tight, but not too tight, fitting a finger underneath the collar before clipping that leash on and tugging on it a little.]

That's a good boy~