God is the only necessarily existing being, as St. Thomas Aquinas shows in his third proof for the existence of God (Summa Theologica I q. 2 a. 3 c.; cf. ch. 3, § "The Third Way" of Aquinas: A Beginner's Guide):
…not all beings are merely possible, but there must exist something the existence of which is necessary. … we cannot but postulate the existence of some being having of itself its own necessity, … This all men speak of as God.
All creatures are a product of God's free will (Summa Theologica I q. 19 a. 4 "Whether the will of God is the cause of things?" c.):
We must hold that the will of God is the cause of things; and that He acts by the will, and not, as some have supposed, by a necessity of His nature.
Nothing necessitates or forces God to create the angels, universe, animals, souls, humans, or any other creature. Therefore, we are all accidents; our being/existence is not necessary.
Regarding what you call "permissive will" and "perfect will",* there is only one will in God; He is supremely simple
. The will of God is always fulfilled
, but a distinction must be made—between absolute necessity and conditional (ex suppositione
or "suppositional") necessity—when addressing the question of "Whether whatever God wills He wills necessarily?
There are two ways in which a thing is said to be necessary, namely, absolutely, and by supposition. We judge a thing to be absolutely necessary from the relation of the terms, as when the predicate forms part of the definition of the subject: thus it is absolutely necessary that man is an animal. It is the same when the subject forms part of the notion of the predicate; thus it is absolutely necessary that a number must be odd or even. In this way it is not necessary that Socrates sits: wherefore it is not necessary absolutely, though it may be so by supposition; for, granted that he is sitting, he must necessarily sit, as long as he is sitting. Accordingly as to things willed by God, we must observe that He wills something of absolute necessity: but this is not true of all that He wills. For the divine will has a necessary relation to the divine goodness, since that is its proper object. Hence God wills His own goodness necessarily, even as we will our own happiness necessarily, and as any other faculty has necessary relation to its proper and principal object, for instance the sight to color, since it tends to it by its own nature. But God wills things apart from Himself in so far as they are ordered to His own goodness as their end. Now in willing an end we do not necessarily will things that conduce to it, unless they are such that the end cannot be attained without them; as, we will to take food to preserve life, or to take ship in order to cross the sea. But we do not necessarily will things without which the end is attainable, such as a horse for a journey which we can take on foot, for we can make the journey without one. The same applies to other means. Hence, since the goodness of God is perfect, and can exist without other things inasmuch as no perfection can accrue to Him from them, it follows that His willing things apart from Himself is not absolutely necessary. Yet it can be necessary by supposition, for supposing that He wills a thing, then He is unable not to will it, as His will cannot change.
cf. Charles De Koninck's "The Problem of Indeterminism" (also on PDF pp. 366ff. of this) and "Reflections on the Problem of Indeterminism" (ibid. pp. 412ff.)
In other words: God wills that some causes produce their intended effects only some of the time. This is not always due to a defect in the cause but can be due to a defect in the effect (ibid. ad 4):
that God does not necessarily will some of the things that He wills, does not result from defect in the divine will, but from a defect belonging to the nature of the thing willed, namely, that the perfect goodness of God can be without it; and such defect accompanies all created good.
For another treatment of the question, see St. Thomas's Summa contra Gentiles I cap. 81 "That God Does not Will Other Things in a Necessary Way".
*St. Thomas nowhere uses the term "perfect will", but he does distinguish between "five expressions of will—namely, prohibition, precept, counsel, operation, and permission" (Summa Theologica I q. 19 a. 12).