Saint Seiya is a series that it has various works based on it. And all of them add a little flavor to the mix and even inspiring future works on various things.
I guess that if I could compare it to something it would be to Senran Kagura, where there are two universes (the main one and the versus one) and still even if they are separated realities, one complements the other with some knowledge or opening certain themes or lore.
Something like that happens between The Saint Seiya Series .Where some elements are grabbed by the other authors and implement them on their own works.
Let us check them.
Deities and their vessel
The Concept was first introduced in Saint Seiya. When Julian Solo was taken by Poseidon, and then expanded on Hades, and so forth.
While at the beginning the human whose destiny was to be a vessel of the Gods lost all of his personality Shiori on her work “Saint Seiya –The Lost Canvas- “took another take on on such event. By making that even if the Deity was inside, they would adopt the personality and traits of the person who were before.
As an example we have: Hades with Alone where Hades acted as Alone with all of his nobility and charm, basically he was a some form of Psychopath or Serial killer vibe…Of course there it was certain explanation for it, which I won´t say since it is spoiler.
Chimaki Kuori then would take such thing and do it too on the case of Eris with Kyoko, where Eris now not only looks like Kyoko; but acts and speaks like her!
This is a clear evolution of such event that started quite simple with Kurumada and later evolved in something truly interesting that gives a new dimension to the Saint Seiya Deities.
God Sealing/Killing Objects
On Saint Seiya there are certain objects whose nature is divine, and they are the only way one can truly damage a Deity, not only the body where they are, but truly make damage to the God.
These objects are varied and their number has been increasing with the pass of the years.
Still…Not every object can damage or seal any divinity. Some work with some Gods and other objects with other divinities.
At first there was only the Sagittarius Arrow and Athena´s dagger, the first one was to damage any God, while other to kill Athena.
Later the Poseidon´s Urn and the Hypnos/Thanatos Box appeared, that are places where such divinities sleep until they are awakened either by chance or fate.
The Athena seals appeared later which serves as some form of barrier of protection.
Other objects later appeared too like the Aioros Memento and Draupnir (Soul of Gold) The Chain of flowers (Lost Canvas) and more…
There it is to say that most of those objects have been respected in one way or the other especially the ones who appeared on the original Saint Seiya. And their properties continue to be respected.
On the same note.the Armors can become on a Divine state, where they are more powerful than even a Gold one and well… The user is able to damage and defeat Gods with it. These especial armors are only temporal and will only stay until their mission is accomplished, something that can be seen in Next Dimension and Soul of Gold.
Family and newer Generations
While it is hard to believe, specially seeing the art of Saint Seiya, most of our Young Heroes aren´t even on their 20´s. Still some authors have decided to plan a somewhat what was for our Heroes when they became adult.
Besides that some of them will become Gold Saints, one of the points that I liked (especially in G: Assasins) is that even though they are Gold Saints they have a life outside the Sanctuary.
-Shun will become a Doctor.
-Hyoga Bartender and will have a daughter.
-Shiryu an Importer/Exporter and will have at the very least one son.
-Ikki´s whereabouts are unknown.
-Seiya is a mystery.
Still some of those family relationships in the Spinoffs have inspired even kurumada.
Talking specifically about Shoryu and Ryuho.
Ryuho is the blood Son of Shiryu and Shunrei in the Spinoff Saint Seiya Omega. The idea of Shiryu having a child truly liked Kurumada and decided to add it in Next Dimension. Still, as said earlier, they are very young, so it is not time to have children! So in order to avoid a Teen Pregnancy scenario he decided to give him an Adoptive child.
Shoryu…Who is still a baby, so yeah, he doesn´t do much.
These are only some samples about the things that in the Universe of Saint Seiya have passed and together have brought some lore and light to some things that surround that Universe.