I know people already commented similar things probably, but yes, Seto will be a bit of a Lawful Evil character. Definitely will cause conflict down the line, with Michiru and/or Miko's dad, both of which would affect Miko. The reason is obvious. First of all, Seto is saying he "can't see anything in the photo" and is saying "the photo just looks to show a normal girl". This seems innocent at first glance since the context of the photo-spree was to focus on Michiru, but on the other hand, that also means he might not even know the "unassuming, janitor-looking-ghost" is even the thing that's foreboding Miko & Romm's fate. We didn't get to see the full elevator conversation and what Romm actually tells Seto, after all, and how Seto interprets it. What if the only information he knows is that "there is a terrible evil spirit in the photo", but he doesn't know where it is? Even if his Quintet-Mafia-Entourage tells him, is their judgment properly on the unassuming one, or Michiru's tentacle spirit?
It's very likely that when he tries to "take care of the issue" this happens: He thinks it's simply close to Michiru -> Be in proximity with her tentacles -> kills it without a second thought -> stuff ensues.
This would parallel what he did with the ghost kid in the station. He hears there's a little trouble around that place, spots a spirit, kills it instantly.
Second important thing is yes, he did say "(Miko) is a sweet girl. Just like Mitsue and Romm. that's why my heart aches; because I'm always on the side of the people".
It's worth remembering that Mitsue and Romm, in earlier chapters and flashbacks related to the mountain god for example; are shown to be mediums who WOULD help ghosts at least half the time. Partially, as Romm himself said, because they have the experience to know "when to talk with the spirits" and decide that they can do something. Romm with hearing a call for help on from the mountain shrine and deciding to go there as a kid. Mitsue helping a gambler husband realize that her wife still watches him from beyond and that he should turn his life around. Even Miko has been shown to help some ghosts from time to time, even if not intentionally. The forgetful grandma in the neighborhood(?) that ends up being able to open the late husband's safe / conversing with the hospital kid. These all show a nuanced, gentle personality that might be willing to consider alternatives and not see "rules" in a rigid way.
So it's very clear to me that Seto's contrasts with the 3 of them is that he will, almost always, without any hesitation kill every ghost he comes across, as his personal rule or value. It should already be apparent so far. He also says "You can't really know what's going on when you hear things from someone else". This line might drive the fact that he can't bother having "nuance" since all his knowledge comes from his Quintet-Mafia-Entourage, but this line serves an additional purpose; it also means he can't TRUST other medium's judgment. Even if Miko, Mitsue or Romm all know Michiru and tries to say that this kind of tentacle-ghost would never harm people, or if Miko says she's been fine with her dad's ghost roaming around the house and it's even helpful as a protector for her, Seto simply cannot trust any of it. After all, he also thinks "looks can be deceiving".
