I'd like to take a quick examination of that Mari conversation from another, more serious angle. Key perspective: Everything Mari did was intentional and had the desired effect.
"Right. If nothing else, think about the impression that it gives of us to those beings. Assuming they think, but let's assume the worst and be pleasantly surprised if it's not the outcome. If those things think and they ever make it into our reality, they're going to assume that all human are murderous warmongers focused solely on killing each other."
Mari's lips twitched. "I mean...they wouldn't be wrong."
"C'mon, Mari. Be serious."
"I am serious...well, I suppose 'killing' is too far. Dominating? Enforcing our will upon? Power. That's the only thing that anyone really cares about, Hazō. Ninja or civilian, clan or not, everything is about power."
Here's where the conversation first goes off the rails. Hazou's presented the main thrust of his take, and Mari's remarked that it's worrisome but does make some things make sense. And then she drags Hazou's attention to a statement about human nature. From our key perspective, there's a reason why Mari derailed the conversation. We'll get back to that in a moment.
She looked over at him, her eyes serious. "Think about it, Hazō. Why does a baby cry? Because it wants to force its parents to provide something—food, warmth, cleaning. It wants to impose its will on the world. Why do merchants haggle? Because they want to exert power over the customer by forcing him to give up more money. Why do ninja kill each other? Because murder is the penultimate form of power. Jiraiya was the perfect example: Everyone did what he told them to because he could kill them. He had power, they didn't."
Mari chuckled. "Oh, Hazō. My sweet summer child. You think sex isn't about power? Sex is the ultimate form of power. Were you not paying attention when I made Wakahisa shoot every one of his secrets right out his dick?"
The derail takes the form of various baits that rub Hazou the wrong way and compel him to make a counter, even though it leads him further away from what he wanted to be talking about. In addition, the derail trends onto sex and power, a distinctly awkward and uncomfortable topic for someone like Hazou.
"I went to those market with this eye-catching hair loose around my shoulders." She twirled a fire-red strand demonstratively. "I put liner under my eyes to bring out the green. I painted my lips red and wore a bra that had my tits about to spill out. Do you think I would have gotten the same prices if I covered up and bound my tits flat? Beauty is about power, just like sex."
This conversation had gone so far off the trail, Hazō wasn't even sure that he was on the same map. What he was certain of was that he didn't want to be having it anymore.
Mari eyed him for a moment, her smirk all but shouting her awareness of the fact that he had retreated in disarray from their prior topic. Fortunately, after a moment she decided to let it go.
The derail plays out in full detail, until Hazou's voiced every objection and been shot down by Mari (not that she's correct, of course, just that she countered Hazou's objections) and Hazou retreats. Social loss.
"Okay. Say you're right. So what?"
"It's all tied up in what I've been worrying about with reality being in danger. If those entities were to break out of whatever prisons they're currently in, how much damage could they do? They could destroy everything."
Mari chuckled and stood up, collecting her book from the table. "They won't."
"How do you know?"
"Because you'll stop them." She smiled and rested her hand on his shoulder for a moment. "Good night, Hazō."
She walked away, leaving him alone with his thoughts in front of the fire.
By comparison, the rest of the conversation finishes in the blink of an eye, with Mari not giving Hazou much help clearing his mind. "Because you'll stop them." is a nice touching statement of confidence but it isn't actually a meaningful thought on what he ought to do
to stop them, or how that slots into his greater priority scheme for fixing the world.
If we assume that Mari knew what she was doing when she did these things (likely), and that she thus willingly chose to do so, I get the impression of a Mari who
does not want to be having this conversation. She lets it run long enough to hear the main thrust of his concern, enough that he can't feel like he didn't share his concerns, and then distracts him with a digression that sets him off-balance for a while, and then ducks out without giving Hazou what he wanted.
Beyond that, I'm not sure. Is she just tired of thinking about the horrors beyond reality that may or may not kill everyone sometime down the line, and wanted to shut Hazou up without appearing to be doing so? Is she trying to encourage Hazou to think about this himself instead of relying on Mari for guidance? Does she really just think there isn't much of a point having the conversation, because she has faith that Hazou will find some way to stop it from becoming an issue? To be honest, none of those really ring true to me, but I don't have a better hypothesis.
The second question is why she chose to derail in the way that she did. She baited Hazou into disagreeing with her on human nature, in an uncomfortable and awkward domain, and handily shot down his arguments until he backed off. Assuming this was intentional, why did Mari want this to happen? Was it a power play, forcing Hazou onto bad footing, forcing a social failure, and asserting herself as the more capable party? Did she just want to convey some of her philosophy on power to Hazou, and chose a terrain that would give her the best advantage in doing so? Once again, I'm not completely happy with either option, but I don't have any better alternatives on-hand.
Lastly, why did she leave Hazou like that? It's barely no help at all, just shy of actively hindering. She essentially says 'yeah, that sounds bad, but you'll figure out a way to take care of it'. As mentioned earlier, she doesn't help him figure out how much he should focus on this or not, or help figure out how he'd go about stopping such an eldritch horror. She just leaves the tasks to him, both figuring out how much he should care and what measures he would take if he does decide to care. This could be Mari training Hazou to not rely on her, and to figure out things for himself as Clan Head. That perspective doesn't jive with some previous options, like 'force Hazou to Social Loss to assert her own authority', but even if those options are mutually exclusive that doesn't rule either out.
Sorry for the rambly and entirely not quick examination, but I think there's important information to glean from this scene if we take a good look at it. What are your thoughts?