Jason and Neri grew closer through all four seasons, but it became very obvious in Season Four. Cue much teasing.
Neri: Jason says we must be careful now, stay where it is hard to find.
Mera: And if Jason says so, it must be right, hmm?
Neri: Jason cares for us.
Mera: Almost as much as you care for him.
Neri: You make big talk about nothing.
Jason invites himself to spend the night with Neri and Mera. They gang up on him.
Jason: Something funny?
Mera: Just how you always agree with Neri.
Jason: I only agree with her when she's right.
Mera: In that case she must always be right.
Jason: Yeah, well, she is, um, alm - almost always right.
Neri: Oh? When am I wrong, Jason?
Jason: Well, you know, we all make mistakes sometimes...better turn in, hey?
Neri: Jason, I'm glad you are here. Goodnight.
Jason: Night, Neri.
Mera: (several moments later) Goodnight, Jason.
Jason: (coughs) Night, Mera.
Season 1 gives us Damien, who in all his daggy glory, manages to start off his Character Development episode...with an eating contest. He then later manages to rescue Lee (by running his guitar through the circuits powering the locks) and offers to demonstrate how he did this to a group of fangirls...only for the circuit to blow.
In a second season episode, Neri is wandering around on ORCA while Jason and a few others are off visiting the institute where Mera had been taken to. Mick decides to pull the classic "glue a coin on the floor" prank on Rocky, only for Neri to reach down, pick it up off the floor as though it was sticky tape, and hand it to Mick.
In the Season 2 finale (and possibly implied to have been the original end of the series had they not made two more), the kids (and adults) manage to put together a plan to get Neri and Mera to the alien ship on the island, all the way from ORCA and through a heavily guarded line of UBRI boats, using a decoy. When Hellegren catches up with the decoy boat however, he discovers that the two "girls" on there are not only decoys, but one of the girls isn't a girl! It's Mick.
Mick's line in that same scene is priceless.
Cass and Brett's "Prank war" during the early part of Season 3.
Dianne's absolute smug face in Season 3 when she manages to foil Kellar's plan to replace Winston (who couldn't swim or dive at the time) is a Funny Moment in itself.
Season 4 gives us one in the first episode when Jason proceeds to hold up a shell to catch some dripping water, all while running his mouth off about the hut Neri now lives in. Cue a creak and then the roof caves in, pouring water over him and extinguishing the fire. Jason can only muster a "What are you laughing at?" moment.