I answer that, As stated above (Article 6), anger desires evil as being a means of just vengeance.
This is a real problem, but we'll roll with it for now. A relationship of justice between you and whatever you're angry at (or vice versa) would seem to need to exist, because if there were no justice relationship you would presumably not be angry at having justice violated. That part is straightforward.
But what is a 'justice relationship'? Aristotle and I disagree about where justice arises in human relationships. For Aristotle it appears to arise at the level of politics, not at the level of family or individual relationships as between father and son. Indeed, Aquinas quotes him saying that in this article: "Further, "there is no justice towards oneself . . . nor is there justice towards one's own" (Ethic. v, 6)."
So here's what Aristotle says at Aquinas' 'link' to the EN:
For justice exists only between men whose mutual relations are governed by law; and law exists for men between whom there is injustice; for legal justice is the discrimination of the just and the unjust. And between men between whom there is injustice there is also unjust action (though there is not injustice between all between whom there is unjust action), and this is assigning too much to oneself of things good in themselves and too little of things evil in themselves. This is why we do not allow a man to rule, but rational principle, because a man behaves thus in his own interests and becomes a tyrant. The magistrate on the other hand is the guardian of justice, and, if of justice, then of equality also. And since he is assumed to have no more than his share, if he is just (for he does not assign to himself more of what is good in itself, unless such a share is proportional to his merits-so that it is for others that he labours, and it is for this reason that men, as we stated previously, say that justice is 'another's good'), therefore a reward must be given him, and this is honour and privilege; but those for whom such things are not enough become tyrants.
The justice of a master and that of a father are not the same as the justice of citizens, though they are like it; for there can be no injustice in the unqualified sense towards thing that are one's own, but a man's chattel, and his child until it reaches a certain age and sets up for itself, are as it were part of himself, and no one chooses to hurt himself (for which reason there can be no injustice towards oneself). Therefore the justice or injustice of citizens is not manifested in these relations; for it was as we saw according to law, and between people naturally subject to law, and these as we saw' are people who have an equal share in ruling and being ruled. Hence justice can more truly be manifested towards a wife than towards children and chattels, for the former is household justice; but even this is different from political justice.
We should note immediately that most Americans -- at least -- would object to the formulation that a master cannot be unjust to his slave because the slave belongs to him. Most of us would argue that the master is already being unjust to the slave by pretending to own him. The Bible speaks of slavery a great deal, and does not categorically reject it as we; but in Aquinas' day the Church had moved to ban the practice between Christians as fundamentally unjust given the special equality Christians had as brother sons of God.
Since you were supposed to try to save souls, if you encountered non-Christians you were supposed to convert them rather than enslave them.
Also, I note that it is only at the level of politics coming to be that this kind of injustice is possible. There might be a natural capacity to enslave another, but there can't be a natural right to do it because the other has the same nature as you: a rational human being. If you have natural rights to freedom, he must as well. It is only the rise of positive law that creates this kind of injustice, and enshrines a 'right' to do this as a master and owner rather than just another free man.
Therefore, I submit that Aristotle is wrong about where the justice relationship properly arises: that it arises not at the political level, but at the level of personal relationships. These are also, sadly, often the place where we most regularly and intensely experience anger. We may be unjust to each other there, too; but at least we do not have armies and towers and systems of justice standing over us and telling us that we must submit to a law that renders us a slave.
But set that aside: would we accept that a father cannot be unjust to his children? We would not accept that. There are many duties we think a father owes to his children, and failure to provide those things is an act of injustice. If you starve your children rather than feeding them, that is unjust. If you drink up the family wealth, you have acted unjustly and deprived your young sons of the standing they had a reason to hope to have when they became adults and masters of themselves.
For the purpose of the consequences of this bad argument, it is certainly not true that you cannot be angry with your children -- which would follow if we accepted Aristotle's argument. Since you cannot have a justice relationship with them -- and cannot be unjust to 'your own' -- it would therefore be impossible to be angry with them. This is manifestly untrue. I daresay no parent has ever raised a child without being angry at them, and vice versa.
It is also not true, as Aristotle says and Aquinas endorses, that you cannot be angry with the dead.
"...according to the Philosopher (Rhet. ii, 3), 'it is impossible to be angry with insensible things, or with the dead': both because they feel no pain, which is, above all, what the angry man seeks in those with whom he is angry: and because there is no question of vengeance on them, since they can do us no harm."
This is another area disproven by human experience. Many times we are angry with the dead; although, unlike Aristotle, we are not obligated to imagine them as being free from all possibility of vengeance or pain. Yet even if we do so imagine them, often we are angry at them because of their tragic choices, and the harm and injustice they have done. This can certainly last well beyond the fact of their death.
In any case, this article strikes me as going wrong in a number of places. It relies on one of Aristotle's mistakes -- he was human, however great his mind, and made a few. That leads to bad consequences for our understanding.