Question: I'm running a Hero-level Scion game where several characters have been breaking all sorts of laws while still staying within their Virtues. I want them to encounter a Demigod who focuses on Justice and can deliver some righteousness on them if need be. However, they mainly focused on their Epic physicals and rarely if ever use Willpower or their Virtues. Is there really anything I can use against them besides Star Chamber?
First of all: we've heard you guys. Justice's low levels suck. We have put it on the giant list of Things That Need Fixing, and hope to do so sometime before the death of the universe. But in the meantime, let's look at what we can do here as a Demigod-level Scion.
To begin with, while not using Virtues might take some of the low-level Justice powers out of the game, bleeding Scions of their Willpower can still have a major impact. There are powers that cost Willpower, and even if they don't have any of those, having no Willpower will make them very prone to Virtue Extremity. Justice isn't the only thing that can de-Willpower a Scion; your just-beatdown-minded Demigod could also employ knacks like Opening Salvo, Scathing Retort or Knowing Glance. If you're really looking for ways to make sure these Scions suffer some of the consequences of their actions, they don't even have to break their Virtues; if they're low on Willpower and the Demigod punishing them breaks their Virtues, they'll have just as much of a spiritual crisis on their hands.
But anyway, on to the main event: Justice boons and how to use them on people who don't care about anything but their punching stats. First of all, if there's a particular misbehavior that your Scions are often guilty of that isn't technically illegal, you'll want to give this Demigod Code of Heaven so he can kick their asses even if they haven't strictly broken a law. If one of their favorite shenanigans is listed on the Code of Heaven table, consider making your Demigod from that pantheon so that they have a free ticket to clock these kids one if need be. This prevents the dreaded Lawyering.
Punishments in the Justice purview often depend on what the person did and what your goal is in punishing them. Are you trying to make them realize there are consequences for doing that thing, or just consequences for misbehaving in general? Are you trying to rehabilitate them, or just slap them one for being bad? Are you trying to punish them as in doing something that inconveniences them, or something that devastates them, and is it okay with you to punish them in a permanent way, or are you trying for something severe but temporary?
Depending on the answers to those questions, you have several options. Scarlet Letter is a hilarious good time, and while it won't necessarily prevent them from enjoying their beating-stuff stats, it can instantly torpedo their social interactions, or at the least very thoroughly embarrass them and make others not trust them as much. Banish is a great choice for use against a Scion in a retaliatory way; it keeps them away from whatever it is they may have just screwed up, and can be vastly inconvenient or dangerous for them, especially if they have to do things within that banishment area, and instead they're separated from some of their group and can't help the mission succeed or ride to anyone's rescue (or have anyone else nearby to rescue them, for that matter). At best, the whole group will have to stay outside the area of the banishment until he can participate, which will suck and possibly make them miss windows of opportunity, and which often gets the whole group on the "let's not do that again" bandwagon since they were all affected even though only one person actually had the boon used on him. For the high-level Justice Demigod, Psychic Prison is an absolute devastation maneuver; it not only causes significant psychological harm to the person it was used on (but actually only takes a few minutes of real time to happen, so whatever mission they're on isn't even impeded!), but also drains away social stats to represent that damage. These may be primarily physical Scions, but I'd lay odds that at least some of them would not be pleased to suddenly lose dots they previously possessed. And, also at that high level of Demigodhood, Sanctify Oath is another bombshell, and visits endless botchery on Scions who break promises (which the Demigod should, of course, ask them to make when he suspects they're going to misbehave).
However, for a whole group full of mostly physically-oriented people who need a love-tap from Justice, I think your best possible choice might be Sympathy Pains, which ties several people together so that all of them suffer pain and damage simultaneously. Tie them to innocent bystanders, so that if they get hurt everyone suffers; tie them to their enemies, so that they have to accept their punishment if they want to win the day; tie them to the Demigod himself, so that he's untouchable to them unless they want to punch themselves in the face. Sympathy Pains is designed to be used against physical characters who think with their fists and need to be reined in by forcing them to confront that what they do hurts others, so it's flexible enough to be used in a lot of situations for these characters.
Of course, they may find a way to pull one over on your Justice-y Demigod, and if so, well, them's the breaks - sometimes the PCs take out a lovingly-crafted NPC, and that's that. But since Justice is designed to deal with people who have managed to get away with some bullshit in spite of their other obligations or Virtues, using it on Scions who are consistently being dicks is just the way the gods intended things to be.