There's a flicker of something when Katsuya touches the door. Verity can clearly see the image through the glass change at his touch from the station to the Nexus. One of the benefits of seeing through illusions is you never miss a way back out of any dimension you pop into.

For Katsuya, who doesn't have any such ability, he hesitates for a different reason. A sinking feeling that Helios gives when the door is pulled open. It's concerning, but for an altogether different reason than their visit ending. Katsuya peers inside to the Nexus when the door is open before holding his hand out for Verity to take as they leave Sumaru altogether. He seems to be in a hurry somewhat to close the door. He really is worried about strangers getting into his home or what could come out of that door.

"Please message me when you'd like to meet up, okay?" Katsuya pulls his phone out and gestures to it. "Or even if you need something in the Nexus." If she needs him, he'll be there. Sometimes it's difficult to translate in his head exactly what he means to say.