[Fukuda's perceptive nose might have spoiled the surprise, but! What his nose probably can't pick up is that the man he sounds delighted to meet is armed with a knife.]

Wow, you figured it out. That's quite sharp of you...

[Lunging himself at the taller man in a swift motion, Saito pins him to the one of the walls surrounding them, using both his own weight and arm to restrain his senior's movements. A crazed smile taints his features as he lifts his armed hand to Fukuda's neck, bringing the blade of the knife to rest against the sensitive flesh of the man's throat. Saito chuckles as he leans in, voice a velvety whisper.]

... But also pretty stupid. Your carelessness could cost you your life, you know?

[Of course this is mostly a bluff. A prank he wanted to try out, given the opportunity. The intention is very much real, though, and it's the high risk of consequences, not his (semblance of a) relationship with the other man that stops him from following through with the threat.]