Kai would 100% burst into tears if "Are you okay?" left the Farmer's mouth.
I think Kai is a tough guy to make crack to cry. But it could be such a tender moment, and would have to be a build up of emotions that Kai has been resistant to express. Kai has been in survival mode since it was just him and Kai - young kits out in the wilderness and having to fend for themselves after the death of their parents. Certainly, Grimshire must have lent their support, but there are some things only Kai as the older brother could understand as a survivor and a guardian to the only family he has. He must feel as if he needs to shoulder all of this, on himself.
Survival was as rewarding as much as it was punishing - scrapes, bruises, empty bellies - but it had to be worth it in contrast with the joy of a large catch or a bushel of fennel, the grin of his younger brother and the swell of pride as they could sit beside their fire pit with full stomachs. Kai must of had to shove down the grief and stress for the sake of making sure Tano, didn't have to face the brunt of suffering. He can't afford to be weak. He could dampen such feelings when he had the routine and rhythm of survival to preoccupy him.
With the events of Grimshire, however, I can see things turn on its head. As soon as the Red Tide pulls in, so does Kai's anxiety. He calculates how much dried fish they have to live off of before their larder runs out, where to fish and hunt away from the Hunt, how much to ration (I always imagine Kai gave the largest portions to Tano, a point of contention between them now that Tano is old enough to know his brother's self-sacrificing habits), and by Anima, how to make sure Tano doesn't get sick. In my mind, Tano is always the priority for Kai before himself.
Then there's the beast in the woods, and I'm sure a majority of us can imagine the spike of anxiety Kai and Tano may have. The increasing threat of starvation and the thought of death looms over all. The Lynx Brothers are far more exposed to what beasts there may be, and Kai probably takes watch every night during that event. Sleep doesn't come easy, and most certainly won't if that happens to Tano.
So, imagine the Farmer, after tirelessly mining or foraging for the sake of the next town project - to find Kai perched on that incline the Lynx Brother's shelter in the Marsh. Haggard looking, yet eyes gleaming in the dark as the Farmer approaches, spear held tight. What semblance of ease only returns when the Farmer verbally announces themself, and the grip on the spear slackens. But he doesn't let go. His eyes, flicker behind the Farmer in occasion, on edge.
It's dangerous to be out this late. He may say, low and chiding. The Farmer could probably only pose the something similar - Yet here you are. And here is Kai.
There could be a quiet talk between the two, hushed to not wake Tano as they discuss the events of the season and those past. It's only when there's a lull, that the questions turn to Kai - Have you eaten? How long have you been awake? Perhaps the questions start to prickle Kai, already sleep deprived, not wanting to seem weak and briefly thinking the care is judgement. But the soft utterance of Are you okay?
He's silent. Of course he's not. Of course he's hungry, tired, and scared. Scared for Grimshire, scared for his brother, scared for himself. But how can he say those things aloud? Complaining is a luxury, fear is for kits who could hide in the arms of their parents. Yet warm tears slide down his face before he can look away and stop himself, the darkness of night betrays him when he lets out a shuddering breath when he tries to deflect with his answer.
Maybe that's when he and the Farmer sit down, or maybe the Farmer ushers him into a hug to cry into their shoulder, a moment of trust and vulnerability without judgement.