[Because you're nicer than you pretend to be. There's a bit of a pause as Dai considers this before he writes his reply]

Thank you. Do you know the unit number?

[Hm. He's not the swiftest to sense mood in writing but it takes a troll to know another. A couple of thoughtful dots go here.]

You need some help, Daitou-san?

Thank you, Krile-san.

Tian is an adult, no? I am sure that if he wanted to go somewhere, he would simply go and then come back?

Yes? How? Is his chair running away?

No. He's not an adult right now.

[...and a little while later]

It still works.

He may have been taken to the fourth floor.

[still clueless~]