Even after joining the Cleaners, Zanka is kinda too serious. Like, he'll hang out and join in activities and go to whatever little party they throw (even though the parties are always for no damn reason lol) but he's definitely a wallflower and he'll chit-chat but not really do much else.
When he starts dating Jabber, he opens up. A lot. He sings along to the radio in the car, he'll dance a little at the parties, he'll join in on the jokes and games with more enthusiasm.
The first time his team hears him laugh so hard he's wheezing, is when they catch him on a call with Jabber. They eavesdrop, because of course they do.
Jabber's telling some story about an idiot he came across during a job and Zanka is just. Giggling. Madly. And Jabber goes on and on, and eventually he gets to the best part of his story and Zanka loses it. Full on hysterics, bent over and gripping the table for support, face red as hell and barely able to take a damn breath.
And Jabber was the one to do it.
After that, they don't mind Jabber as much. Because if he can get Zanka of all people to chill out then he can't really be that bad, right?