It's kind of easy to grab Kaori's attention. Either because he's so familiar with the particular things Francis had set up or because it's just kind of a weird place to paint in general, he finds himself watching the other, though he doesn't approach. 
After a while, it's kind of easy to see that he's basically the only one in the immediate surroundings who isn't moving, though, especially if the other guy is looking around and trying to find inspiration in the settings.

Surprise clearly manifests itself on Kaori's face like "Why me?" mostly because he has no distinguishing features to him, really, other than general indications of malnutrition. 
"Uhm, sure!" he answers, making his way carefully over to Francis. For good reason. He's fallen quite a bit times just from strong gusts of wind. 

Kaori wonders if he'd ruin the painting if his knees buckle. He spends a good few seconds trying to ponder if he'll be able to keep standing up before deciding he should just lean on something nearby. Fortunately, there's a tree that's planted and secured nearby, so he kind of just ventures there and places a hand on it to test it. Once he thinks it won't be easily taken down by his weight, he slightly leans against it. "Is this alright?" he asks curiously.

"Alright," he says. "Please let me know if I falter or something like that." He tries to steady himself a bit. He's mostly not shaking, which is good but also kind of questionable. 

"I'm alright," Kaori insists calmly. "I just need to get more used to standing. Thank you for your concern, though."

"I'm doing pretty well," Kaori answers typically but sincerely. "How are you, sir?"

"That's good to hear," Kaori states with a reciprocated smile, and then he tries to stand still again.

"Oh, nice to meet you, Francis. I'm called Kaori," the teenage-looking young man says with his ever-constant smile.

"Thanks!" He smiles a bit more, but not too much. Even though he's aware facial expressions aren't actually very prominent until later on, he'd like to leave a semi-constant impression so the job is easier for Francis.

"I agree on both counts," Kaori states placidly. With his company, it kind of seems like quiet is natural and not awkward at all, but then again, that likely goes for Francis too. On Kaori's end, though, it's kind of like he gives off an attracting peace as his aura.

R.I.P. the conversation, but Kaori's standing there naturally, or as naturally as he can stand, that is, when it kind of feels like he hasn't stood for years. And he hasn't, to be honest, if the comparison is to the recent month or so.

Kaori tries to think of something to talk about, but he's also not too keen on interrupting Francis' humming, so even if he thinks of something other than topics Francis probably wouldn't like to talk about, he doesn't say it.

Kaori honestly wants to question why the butterflies are there just out of his pure sense of logic--they're in the middle of a city, after all--but nothing is impossible, including the presence of entities that are there for roleplaying convenience. But the logic, dull and traditional, is quickly succeeded by emotion.
"Are those monarchs?" he asks rhetorically with an awe that could only be described as childlike. His eyes sparkle with delight and his mouth starts quickly towards forming an elliptical shape. He'll notice he forgot to nod later, don't worry.

Kaori's expression changes towards a gentle one, his eyes filled with warm light. Almost as if he were somehow a monarch butterfly himself, like one of their family members, he muses, "I wonder how many of their one hundred miles they have left to travel today."